Communication Method And Communications Apparatus

ABSTRACT

This application provides a communication method and a communications apparatus, to help control switching of a PDU session, thereby improving system performance. The method includes: determining, by a network device based on switching indication information of protocol data unit PDU sessions established by a terminal in a first network, a target PDU session from the established PDU sessions, where all the established PDU sessions have a same data network name DNN; and sending, by the network device, session information of the target PDU session to a mobility management entity device in a second network.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/CN2019/071718, filed on Jan. 15, 2019, which claims priority toChinese Patent Application No. 201810037209.3, filed on Jan. 15, 2018.The disclosures of the aforementioned applications are herebyincorporated by reference in their entireties.

TECHNICAL FIELD

This application relates to the communications field, and morespecifically, to a communication method and a communications apparatusin the communications field.

BACKGROUND

With rapid development of wireless communications technologies, a fifthgeneration (5G) mobile communications technology emerges. In an initialnetwork deployment phase, because of insufficient coverage of a 5Gnetwork, when a location of user equipment (UE) changes, the UE needs toswitch a session between the 5G network and a fourth generation (4G)network.

An access point name (APN) parameter is required when a packet datanetwork (PDN) connection is being established in the 4G network, and adata network name (DNN) is required when a protocol data unit (PDU)session is being created in 5G. The APN in 4G is equivalent to the DNNin 5G.

The UE may establish one or more PDU sessions in 5G and the PDU sessionsmay use a same DNN. In addition, it is not specified in 5G that a singlesession management device needs to be selected for sessions with a sameDNN. Therefore, the one or more PDU sessions with a same DNN may beanchored to different session management devices. In 4G to control anaggregated maximum bit rate (AMBR) of the APN, it is required that oneor more PDN connections with a same APN can be anchored to only onesession management device. When one or more PDU sessions with a same DNNare switched, an uncontrolled situation is caused. Consequently, systemperformance is relatively poor.

SUMMARY

This application provides a communication method and a communicationsapparatus, to help improve system performance.

According to a first aspect, a communication method is provided,including: determining, by a network device based on switchingindication information of protocol data unit PDU sessions established bya terminal in a first network, a target PDU session from the establishedPDU sessions, where all the established PDU sessions have a same datanetwork name DNN; and sending, by the network device, sessioninformation of the target PDU session to a mobility management entitydevice in a second network.

Therefore, in this embodiment of this application, the network devicemay determine the target PDU session from the established PDU sessionsbased on the switching indication information of the established PDUsessions. In this way, the target PDU session may be used as a PDUsession that can be switched to the second network, so as to avoid anuncontrolled situation caused when all the PDU sessions established bythe terminal in the first network need to be switched to a same controlplane function network element in the second network. This helps controlswitching of a PDU session, thereby improving system performance.

Optionally, the terminal may establish one or more PDU sessions in thefirst network. Optionally, if the terminal establishes one PDU sessionin the first network, there is one piece of switching indicationinformation of the PDU sessions established by the terminal in the firstnetwork. If the terminal establishes multiple PDU sessions in the firstnetwork, the switching indication information of the PDU sessionsestablished by the terminal in the first network may be switchingindication information of the multiple PDU sessions.

Optionally, the first network is a 5G network, and the second network isa 4G network.

Optionally, the network device is a user data management network elementor an access and mobility management function entity.

In some implementations, the switching indication information is used toindicate a switching priority of each of the established PDU sessions;and the determining a target PDU session from the established PDUsessions includes: determining, by the network device as the target PDUsession, a PDU session with a highest switching priority in theestablished PDU sessions. For example, a switching priority of a PDUsession may be represented by a number. Optionally, there may be one ormore PDU sessions with a highest switching priority.

In some implementations, the switching indication information is used toindicate whether each of the established PDU sessions can be switched;and the determining a target PDU session from the established PDUsessions includes: determining, by the network device when the switchingindication information indicates that there is only one PDU session thatcan be switched, the PDU session that can be switched as the target PDUsession; or determining, by the network device when the switchingindication information indicates that there are at least two PDUsessions that can be switched, the target PDU session from the at leasttwo PDU sessions.

In some implementations, the determining, by the network device when theswitching indication information indicates that there are at least twoPDU sessions that can be switched, the target PDU session from the atleast two PDU sessions includes: if the at least two PDU sessions belongto a same control plane function network element, determining, by thenetwork device, each of the at least two sessions as the target PDUsession; or if the at least two PDU sessions belong to different controlplane function network elements, determining, by the network device, thetarget PDU session from the at least two PDU sessions based onassistance information of each of the at least two PDU sessions.

In this embodiment of this application, the switching indicationinformation may indicate that a PDU session can be switched. If thenetwork device learns that the switching indication information mayindicate at least two PDU sessions, the network device determineswhether the at least two PDU sessions belong to a same control planefunction network element. If the at least two PDU sessions belong to asame control plane function network element, the network device mayswitch the at least two PDU sessions, that is, the at least two PDUsessions are target PDU sessions. If the at least two PDU sessions donot belong to a same control plane function network element, the networkdevice may determine the target PDU session based on assistanceinformation of the at least two PDU sessions; or the network device maydetermine priorities of the at least two PDU sessions based onassistance information of the at least two PDU sessions, and determine aPDU session with a highest switching priority as the target PDU session.

In some implementations, before the determining, by a network devicebased on switching indication information of protocol data unit PDUsessions established by a terminal in a first network, a target PDUsession from the established PDU sessions, the method further includes:receiving, by the network device, assistance information that is of afirst PDU session in the established PDU sessions and that is sent by afirst control plane function network element; and determining, by thenetwork device, switching indication information of the first PDUsession based on the assistance information. Herein, the network devicemay be a user data management network element or an access and mobilitymanagement function device.

Optionally, when the network device is a user data management networkelement, the method further includes: sending, by the user datamanagement network element, the switching indication information of thefirst PDU session to the first control plane function network element.

In other words, the user data management network element may receive theassistance information that is of the first PDU session and that is sentby the first control plane function network element, determine theswitching indication information of the first PDU session based on theassistance information of the first PDU session, and send the determinedswitching indication information of the first PDU session to the firstcontrol plane function network element.

In some implementations, the assistance information includes at leastone of the following: an internet protocol IP (IP) address versioncorresponding to the PDU session, single network slice selectionassistance information corresponding to the PDU session, a session andservice continuity SSC mode corresponding to the PDU session, anallocation and retention priority ARP corresponding to the PDU session,a service type corresponding to the PDU session, and an establishmenttime corresponding to the PDU session.

In some implementations, before the determining, by a network devicebased on switching indication information of protocol data unit PDUsessions established by a terminal in a first network, a target PDUsession from the established PDU sessions, the method includes:receiving, by the network device, the switching indication informationthat is of the PDU sessions established by the terminal in the firstnetwork and that is sent by at least one control plane function networkelement.

In some implementations, the network device is a user data managementnetwork element, and before the determining, by a network device basedon switching indication information of protocol data unit PDU sessionsestablished by a terminal in a first network, a target PDU session fromthe established PDU sessions, the method includes: receiving, by theuser data management network element, initial switching indicationinformation that is of a second PDU session in the PDU sessionsestablished by the terminal in the first network and that is sent by asecond control plane function network element; and adjusting, by theuser data management network element, the initial switching indicationinformation to obtain switching indication information of the second PDUsession; and the method further includes: sending, by the user datamanagement network element, the switching indication information of thesecond PDU session to the second control plane function network element.

In other words, the user data management network element may adjust theinitial switching indication information that is of the second PDUsession and that is sent by the second control plane function networkelement, and may send the adjusted switching indication information ofthe second PDU session to the second control plane function networkelement. A specific adjustment manner is performing adjustment accordingto a local policy. This is not limited in this embodiment of thisapplication.

In some implementations, the session information of the target PDUsession includes an identifier of a control plane function networkelement corresponding to the target PDU session and a DNN of the targetPDU session.

According to a second aspect, a communication method is provided,including: obtaining, by a terminal, switching indication information ofprotocol data unit PDU sessions established in a first network, whereall the established PDU sessions have a same data network name DNN;determining, by the terminal, a target PDU session from the establishedPDU sessions based on the switching indication information of theestablished PDU sessions; and sending, by the terminal, an identifier ofthe target PDU session to a first control plane function network elementby using a mobility management entity device in a second network.

Therefore, in this embodiment of this application, the terminal maydetermine the target PDU session from the established PDU sessions basedon the switching indication information of the established PDU sessions.In this way, the target PDU session may be used as a PDU session thatcan be switched to the second network, so as to avoid an uncontrolledsituation caused when all the PDU sessions established by the terminalin the first network need to be switched to a same control planefunction network element in the second network. This helps controlswitching of a PDU session, thereby improving system performance.

In some implementations, the switching indication information is used toindicate a switching priority of each of the established PDU sessions;and the determining a target PDU session from the established PDUsessions includes: determining, by the terminal as the target PDUsession, a PDU session with a highest switching priority in theestablished PDU sessions.

In some implementations, the switching indication information is used toindicate whether each of the established PDU sessions can be switched;and the determining a target PDU session from the established PDUsessions includes: determining, by the terminal as the target PDUsession, a PDU session that can be switched in the established PDUsessions.

In some implementations, the sending, by the terminal, an identifier ofthe target PDU session to a first control plane function network elementby using a mobility management entity device in a second networkincludes: sending, by the terminal, the identifier of the target PDUsession and a DNN of the target PDU session to the mobility managemententity device, where the DNN of the target PDU session is used by themobility management entity device to determine the first control planefunction network element, so that the mobility management entity devicesends the identifier of the target PDU session to the first controlplane function network element.

In some implementations, the sending, by the terminal, the identifier ofthe target PDU session and a data network name of the target PDU sessionto the mobility management entity device includes: sending, by theterminal, a first request message to the mobility management entitydevice, where the first request message carries the identifier of thetarget PDU session and the DNN of the target PDU session, and the firstrequest message is an attach request message or a session establishmentrequest message.

In some implementations, the obtaining, by a terminal, switchingindication information of PDU sessions established in a first networkincludes: receiving, by the terminal, the switching indicationinformation of the established PDU sessions that is sent by at least onecontrol plane function network element.

In this embodiment of this application, the terminal may receive theswitching indication information of the established PDU sessions that issent by the at least one control plane function network element. Theswitching indication information of the established PDU sessions that issent by the at least one control plane function network element may bedetermined by the at least one control plane function network element,or may be received by the at least one control plane function networkelement from a user data management network element. This is not limitedin this embodiment of this application.

In some implementations, the obtaining, by a terminal, switchingindication information of PDU sessions established in a first networkincludes: sending, by the terminal, initial switching indicationinformation of the first PDU session to a second control plane functionnetwork element, where the initial switching indication information isused to determine switching indication information of the first PDUsession; and receiving, by the terminal, the switching indicationinformation that is of the first PDU session and that is sent by thesecond control plane function network element.

In other words, the terminal may send the initial switching indicationinformation of the first PDU session to the second control planefunction network element. The second control plane function networkelement may adjust the initial switching indication information of thefirst PDU session to obtain the switching indication information of thefirst PDU session, or the second control plane function network elementmay send the initial switching indication information of the first PDUsession to a user data management network element. The user datamanagement network element adjusts the initial switching indicationinformation of the first PDU session, and sends the adjusted switchingindication information of the first PDU session to the second controlplane function network element. The second control plane functionnetwork element sends the switching indication information of the firstPDU session to the terminal.

According to a third aspect, a communication method is provided,including: receiving, by a first control plane function network element,a session establishment request message sent by a terminal, where thesession establishment request message is used to request to establish afirst protocol data unit PDU session; and obtaining, by the firstcontrol plane function network element, switching indication informationof the first PDU session. The first control plane function networkelement may be any one of multiple control plane function networkelements. Session establishment request messages received by theplurality of control plane function network elements may request toestablish multiple PDU sessions, and the multiple PDU sessions have asame DNN.

In some implementations, the switching indication information is used toindicate a priority of the first PDU session or used to indicate whetherthe first PDU session can be switched.

In some implementations, the session establishment request messageincludes the switching indication information of the first PDU session;the obtaining, by the first control plane function network element,switching indication information of the first PDU session includes:obtaining, by the first control plane function network element, theswitching indication information of the first PDU session from thesession establishment request message; and the method further includes:sending, by the first control plane function network element, theswitching indication information of the first PDU session to a user datamanagement network element or an access and mobility management functiondevice.

In this embodiment of this application, if the session establishmentrequest message sent by the terminal to the first control plane functionnetwork element carries the switching indication information of thefirst PDU session, the first control plane function network element mayobtain the switching indication information of the first PDU sessionfrom the session establishment request message.

In some implementations, the obtaining, by the first control planefunction network element, switching indication information of the firstPDU session includes: obtaining, by the first control plane functionnetwork element, initial switching indication information of the firstPDU session; and obtaining, by the first control plane function networkelement, the switching indication information that is of the first PDUsession and that is obtained through adjustment based on the initialswitching indication information; and the method further includes:sending, by the first control plane function network element, theswitching indication information of the first PDU session to theterminal, a user data management network element, or an access andmobility management function device.

In this embodiment of this application, the initial switching indicationinformation of the first PDU session may be adjusted to the switchingindication information of the first PDU session. Specifically, thefollowing several manners may be included. In a first manner, the firstcontrol plane function network element receives the initial switchingindication information that is of the first PDU session and that is sentby the terminal, and the session establishment request message may carrythe initial switching indication information. The first control planefunction network element may adjust the initial switching indicationinformation of the first PDU session. The first control plane functionnetwork element may send the adjusted switching indication informationof the first PDU session to the terminal, for example, send the adjustedswitching indication information of the first PDU session to theterminal by using a PCO. In this way, the terminal may receive switchingindication information of multiple PDU sessions that is sent by multiplecontrol plane function network elements; and the terminal may determinea target PDU session, namely, a PDU session that needs to be switched,based on the switching indication information of the multiple PDUsessions. Alternatively, the first control plane function networkelement may send the adjusted switching indication information of thefirst PDU session to the user data management network element. In thisway, the user data management network element may receive switchingindication information of multiple PDU sessions that is sent by multiplecontrol plane function network elements, and the user data managementnetwork element may determine a target PDU session, namely, a PDUsession that needs to be switched, based on the switching indicationinformation of the multiple PDU sessions. Alternatively, the firstcontrol plane function network element may send the adjusted switchingindication information of the first PDU session to the access andmobility management function device. In this way, the access andmobility management function device may receive switching indicationinformation of multiple PDU sessions that is sent by multiple controlplane function network elements; and the access and mobility managementfunction device may determine a target PDU session, namely, a PDUsession that needs to be switched, based on the switching indicationinformation of the multiple PDU sessions. In a second manner, the firstcontrol plane function network element may receive the initial switchingindication information that is of the first PDU session and that is sentby the terminal, or may determine the initial switching indicationinformation of the first PDU session, and then send the initialswitching indication information of the first PDU session to the userdata management network element. The user data management networkelement may adjust the initial switching indication information of thefirst PDU session to obtain the switching indication information of thefirst PDU session. The user management function network element sendsthe adjusted switching indication information of the first PDU sessionto the first control plane function network element, and the firstcontrol plane function network element may send the adjusted switchingindication information of the first PDU session to the access andmobility management function device. In this way, the access andmobility management function device may receive switching indicationinformation of multiple PDU sessions that is sent by multiple controlplane function network elements; and the access and mobility managementfunction device may determine a target PDU session, namely, a PDUsession that needs to be switched, based on the switching indicationinformation of the multiple PDU sessions. Alternatively, the firstcontrol plane function network element may send the adjusted switchingindication information of the first PDU session to the terminal. In thisway, the terminal may receive switching indication information ofmultiple PDU sessions that is sent by multiple control plane functionnetwork elements; and the terminal may determine a target PDU session,namely, a PDU session that needs to be switched, based on the switchingindication information of the multiple PDU sessions.

In some implementations, the obtaining, by the first control planefunction network element, switching indication information of the firstPDU session includes: sending, by the first control plane functionnetwork element, assistance information of the first PDU session to auser data management network element; and receiving, by the firstcontrol plane function network element, the switching indicationinformation that is of the first PDU session and that is sent by theuser data management network element, where the switching indicationinformation of the first PDU session is determined based on theassistance information of the first PDU session, and the assistanceinformation of the first PDU session includes at least one of aninternet protocol IP address version corresponding to the first PDUsession, single network slice selection assistance informationcorresponding to the first PDU session, a session and service continuitySSC mode corresponding to the first PDU session, an allocation andretention priority ARP corresponding to the first PDU session, a servicetype corresponding to the first PDU session, and an establishment timecorresponding to the first PDU session; and the method further includes:sending, by the first control plane function network element, theswitching indication information of the first PDU session to theterminal or an access and mobility management function device.

In some implementations, the method further includes: receiving, by thefirst control plane function network element, an identifier of thetarget PDU session and a DNN of the target PDU session that are sent bya mobility management entity device in a second network; searching, forthe target PDU session by the first control plane function networkelement based on the identifier of the target PDU session and the DNN ofthe target PDU session, multiple PDU sessions corresponding to the DNNthat are stored by the first control plane function network element; andif the target PDU session is found, selecting the target PDU session forswitching; or if the target PDU session is not found, rejecting thetarget PDU session.

In some implementations, the method further includes: receiving, by thefirst control plane function network element, a PDU session updaterequest that is corresponding to a first data network name (the firstdata network name is a data network name that is of a current PDUsession and that is sent by the terminal to a mobility management entitydevice in a second network) and that is sent by the mobility managemententity device in the second network; and after the first control planefunction network element receives the session update requestcorresponding to the first data network name, obtaining, by the firstcontrol plane function network element based on the first data networkname, a PDU session corresponding to the first data network name. If thefirst data network name is corresponding to one PDU, the PDU session isa session that needs to be switched. If the first data network name iscorresponding to multiple PDU sessions, the first control plane functionnetwork element selects one PDU session as a PDU session that needs tobe switched. The first control plane function network element mayrandomly select one PDU session as a PDU session that needs to beswitched, or determine a to-be-switched PDU session based on assistanceinformation of the PDU sessions. The first control plane functionnetwork element sends an identifier of the to-be-switched PDU session tothe terminal.

In some implementations, the method further includes: sending, by thefirst control plane function network element, a data network name DNN ofthe first PDU session and an identifier of the first control planefunction network element to the user data management network element.Optionally, the first control plane function network element may sendsession information of the first PDU session to the user data managementnetwork element, where the session information includes the switchingindication information of the first PDU session, the DNN of the firstPDU session, and the identifier of the first control plane functionnetwork element. In other words, the first control plane functionnetwork element may simultaneously send the switching indicationinformation of the first PDU session, the DNN of the first PDU session,and the identifier of the first control plane function network elementto the user data management network element. In this way, the user datamanagement network element can store the session information of thefirst PDU session. When receiving session information of multiple PDUsessions (the multiple PDU sessions have a same DNN), the user datamanagement network element determines a target PDU session based onswitching indication information of the multiple PDU sessions, and thensends, to the mobility management entity device in the second network, aDNN of the target PDU session and an identifier of a control planefunction network element corresponding to the target PDU session.

According to a fourth aspect, a communication method is provided,including: sending, by a terminal, a first data network namecorresponding to a current PDU session to a mobility management entitydevice in a second network; and receiving, by the terminal, anidentifier that is of a switched PDU session and that is sent by acontrol plane function network element, and determining the switched PDUsession based on the identifier of the PDU session. Optionally, theterminal receives a PCO sent by the control plane function networkelement, obtains the identifier of the switched PDU session from thePCO, and determines the switched PDU session based on the identifier ofthe PDU session. In this way, UE can associate a PDN connection with acorresponding session.

In some implementations, optionally, the sending, by a terminal, a firstdata network name corresponding to a current PDU session to a mobilitymanagement entity device in a second network includes: sending, by theterminal, an attach request message or a session establishment requestmessage to the mobility management entity device in the second network,where the attach request message or the session establishment requestmessage carries the data network name corresponding to the current PDUsession.

In some implementations, optionally, if the terminal sends, in theattach request message, the data network name corresponding to thecurrent PDU session to the mobility management entity device in thesecond network, after determining a PDU session that needs to beswitched, the control plane function network element switches the PDUsession in an attach procedure. Alternatively, if the terminal adds, tothe session establishment request message, the data network namecorresponding to the current PDU session, after determining a PDUsession that needs to be switched, the control plane function networkelement switches the PDU session in a session establishment requestprocedure. After completing switching, the control plane functionnetwork element sends the identifier of the switched PDU session to theterminal. For example, the control plane function network element sendsa PCO to the terminal, and the PCO carries the identifier of theswitched PDU session.

According to a fifth aspect, a communications apparatus is provided andis configured to perform the method according to any one of the firstaspect or the possible implementations of the first aspect.Specifically, the apparatus includes units configured to perform themethod according to any one of the first aspect or the possibleimplementations of the first aspect.

According to a sixth aspect, a communications apparatus is provided andis configured to perform the method according to any one of the secondaspect or the possible implementations of the second aspect.Specifically, the apparatus includes units configured to perform themethod according to any one of the second aspect or the possibleimplementations of the second aspect.

According to a seventh aspect, a communications apparatus is providedand is configured to perform the method according to any one of thethird aspect or the possible implementations of the third aspect.Specifically, the apparatus includes units configured to perform themethod according to any one of the third aspect or the possibleimplementations of the third aspect.

According to an eighth aspect, a communications apparatus is providedand is configured to perform the method according to any one of thefourth aspect or the possible implementations of the fourth aspect.Specifically, the apparatus includes units configured to perform themethod according to any one of the fourth aspect or the possibleimplementations of the fourth aspect.

According to a ninth aspect, a communications apparatus is provided, andthe apparatus includes a transceiver (which may include a transmitterand a receiver), a memory, and a processor. The transceiver, the memory,and the processor communicate with each other through an internalconnection path. The memory is configured to store an instruction. Theprocessor is configured to execute the instruction stored in the memory,to control the receiver to receive a signal and control the transmitterto send a signal, so that the apparatus performs the method according toany one of the first aspect or the possible implementations of the firstaspect.

According to a tenth aspect, a communications apparatus is provided, andthe apparatus includes a transceiver (which may include a transmitterand a receiver), a memory, and a processor. The transceiver, the memory,and the processor communicate with each other through an internalconnection path. The memory is configured to store an instruction. Theprocessor is configured to execute the instruction stored in the memory,to control the receiver to receive a signal and control the transmitterto send a signal, so that the apparatus performs the method according toany one of the second aspect or the possible implementations of thesecond aspect.

According to an eleventh aspect, a communications apparatus is provided,and the apparatus includes a transceiver (which may include atransmitter and a receiver), a memory, and a processor. The transceiver,the memory, and the processor communicate with each other through aninternal connection path. The memory is configured to store aninstruction. The processor is configured to execute the instructionstored in the memory, to control the receiver to receive a signal andcontrol the transmitter to send a signal, so that the apparatus performsthe method according to any one of the third aspect or the possibleimplementations of the third aspect.

According to a twelfth aspect, a communications apparatus is provided,and the apparatus includes a transceiver (which may include atransmitter and a receiver), a memory, and a processor. The transceiver,the memory, and the processor communicate with each other through aninternal connection path. The memory is configured to store aninstruction. The processor is configured to execute the instructionstored in the memory, to control the receiver to receive a signal andcontrol the transmitter to send a signal, so that the apparatus performsthe method according to any one of the fourth aspect or the possibleimplementations of the fourth aspect.

According to a thirteenth aspect, a service processing system isprovided, including the apparatus according to any one of the fifthaspect or the optional implementations of the fifth aspect, theapparatus according to any one of the sixth aspect or the optionalimplementations of the sixth aspect, and the apparatus according to anyone of the seventh aspect or the optional implementations of the seventhaspect. Optionally, the system includes the apparatus according to anyone of the fifth aspect or the optional implementations of the fifthaspect, the apparatus according to any one of the sixth aspect or theoptional implementations of the sixth aspect, and the apparatusaccording to any one of the eighth aspect or the optionalimplementations of the eighth aspect. Optionally, the system includesthe apparatus according to any one of the ninth aspect or the optionalimplementations of the ninth aspect, the apparatus according to any oneof the tenth aspect or the optional implementations of the tenth aspect,and the apparatus according to any one of the eleventh aspect or theoptional implementations of the eleventh aspect. Optionally, the systemincludes the apparatus according to any one of the ninth aspect or theoptional implementations of the ninth aspect, the apparatus according toany one of the tenth aspect or the optional implementations of the tenthaspect, and the apparatus according to any one of the twelfth aspect orthe optional implementations of the twelfth aspect.

According to a fourteenth aspect, a computer readable storage medium isprovided. The computer readable storage medium stores an instruction,and when the instruction runs on a computer, the computer performs themethod according to any one of the first aspect or the possibleimplementations of the first aspect.

According to a fifteenth aspect, a computer readable storage medium isprovided. The computer readable storage medium stores an instruction,and when the instruction runs on a computer, the computer performs themethod according to any one of the second aspect or the possibleimplementations of the second aspect.

According to a sixteenth aspect, a computer readable storage medium isprovided. The computer readable storage medium stores an instruction,and when the instruction runs on a computer, the computer performs themethod according to any one of the third aspect or the possibleimplementations of the third aspect.

According to a seventeenth aspect, a computer readable storage medium isprovided. The computer readable storage medium stores an instruction,and when the instruction runs on a computer, the computer performs themethod according to any one of the fourth aspect or the possibleimplementations of the fourth aspect.

According to an eighteenth aspect, this application provides a computerprogram product including an instruction. When the instruction runs on acomputer, the computer performs the method according to any one of thefirst aspect or the possible implementations of the first aspect.

According to a nineteenth aspect, this application provides a computerprogram product including an instruction. When the instruction runs on acomputer, the computer performs the method according to any one of thesecond aspect or the possible implementations of the second aspect.

According to a twentieth aspect, this application provides a computerprogram product including an instruction. When the instruction runs on acomputer, the computer performs the method according to any one of thethird aspect or the possible implementations of the third aspect.

According to a twenty-first aspect, this application provides a computerprogram product including an instruction. When the instruction runs on acomputer, the computer performs the method according to any one of thefourth aspect or the possible implementations of the fourth aspect.

According to a twenty-second aspect, this application provides acommunications chip, and the communications chip stores an instruction.When the instruction runs on a terminal, a network device, or a controlplane function network element, the terminal, the network device, or thecontrol plane function network element performs any method in theforegoing aspects.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of an architecture system of interworkingbetween a 4G network and a 5G network according to an embodiment of thisapplication;

FIG. 2 is a schematic diagram of a communication method according to anembodiment of this application;

FIG. 3 is a schematic diagram of another communication method accordingto an embodiment of this application;

FIG. 4 is a schematic diagram of another communication method accordingto an embodiment of this application:

FIG. 5 is a schematic diagram of still another communication methodaccording to an embodiment of this application;

FIG. 6A, FIG. 6B, and FIG. 6C are a schematic diagram of still anothercommunication method according to an embodiment of this application;

FIG. 7A and FIG. 7B are a schematic diagram of still anothercommunication method according to an embodiment of this application;

FIG. 8A and FIG. 8B are a schematic diagram of still anothercommunication method according to an embodiment of this application;

FIG. 9 is a schematic diagram of still another communication methodaccording to an embodiment of this application;

FIG. 10A and FIG. 10B are a schematic diagram of still anothercommunication method according to an embodiment of this application;

FIG. 11A and FIG. 11B are a schematic diagram of still anothercommunication method according to an embodiment of this application;

FIG. 12 is a schematic diagram of still another communication methodaccording to an embodiment of this application;

FIG. 13 is a schematic diagram of still another communication methodaccording to an embodiment of this application;

FIG. 14 is a schematic block diagram of a communications apparatusaccording to an embodiment of this application;

FIG. 15 is a schematic block diagram of another communications apparatusaccording to an embodiment of this application;

FIG. 16 is a schematic block diagram of still another communicationsapparatus according to an embodiment of this application;

FIG. 17 is a schematic block diagram of still another communicationsapparatus according to an embodiment of this application;

FIG. 18 is a schematic block diagram of still another communicationsapparatus according to an embodiment of this application; and

FIG. 19 is a schematic block diagram of still another communicationsapparatus according to an embodiment of this application.

DESCRIPTION OF EMBODIMENTS

For ease of understanding the technical solutions of the embodiments ofthis application, the following first briefly describes technologiesrelated to this application.

The embodiments of the present invention provide a mobility managementmethod, and the method may be applied to an architecture system 100 ofinterworking between a 4G network and a 5G network shown in FIG. 1. Asshown in FIG. 1, the architecture system 100 includes the followingentities shared by the 4G network and the 5G network: a user planefunction (UPF) entity+PDN gateway user plane function (PGW-U) entity, asession management function (SMF) entity+PDN gateway control planefunction (PGW-C) entity, a policy control function (PCF) entity+policyand charging rules function (PCRF) entity, and a home subscriber server(HSS)+unified data management (UDM) entity. Herein, “+” representsintegrated configuration. A UPF is a user plane function of the 5Gnetwork, and a PGW-U is a gateway user plane function, corresponding tothe UPF, of the 4G network. An SMF is a session management function ofthe 5G network, and a PGW-C is a gateway control plane function,corresponding to the SMF, of the 4G network. A PCF is a policy controlfunction of the 5G network, and a PCRF is a policy and charging rulesfunction, corresponding to the PCF, of the 4G network. Herein,“integrated configuration” means that one device has functions of bothof two entities. In the embodiments of this application, for ease ofdescription, the HSS+UDM entity is referred to as a user data managementnetwork element, the PGW-C entity+SMF entity is referred to as a controlplane function network element, and the UPF entity+PGW-U entity isreferred to as a user plane function network element. This is centrallydescribed herein, and is not described again later. Certainly, thenetwork devices obtained through integrated configuration may have othernames. This is not specifically limited in the embodiments of thisapplication.

In addition, as shown in FIG. 1, the architecture of interworkingbetween the 4G network and the 5G network may further include a mobilitymanagement entity (MME), a serving gateway (SGW), and an access andmobility management function (AMF) entity in the 5G network. A terminalaccesses the 4G network by using an evolved universal terrestrial radioaccess network (E-UTRAN) device, and the terminal accesses the 5Gnetwork by using a next generation radio access network (NG-RAN) device.The E-UTRAN device communicates with the MME through an S1-MMEinterface, the E-UTRAN device communicates with the SGW through an S1-Uinterface, the MME communicates with the SGW through an S11 interface,the MME communicates with the user data management network elementthrough an S6a interface, the MME communicates with the AMF entitythrough an N26 interface, the SGW communicates with the PGW-U entity+UPFentity through an S5-U interface, the SGW communicates with the PGW-Centity+SMF entity through an S5-C interface, the PGW-U entity+UPF entitycommunicates with the NG-RAN device through an N3 interface, the PGW-Uentity+UPF entity communicates with the PGW-C entity+SMF entity throughan N4 interface, the PGW-C entity+SMF entity communicates with the PCRFentity+PCF entity through an N7 interface, the HSS+UDM entitycommunicates with the PGW-C entity+SMF entity through an N10 interface,the HSS+UDM entity communicates with the AMF entity through an N8interface, the PCRF entity+PCF entity communicates with the AMF entitythrough an N15 interface, the PGW-C entity+SMF entity communicates withthe AMF entity through an N11 interface, the AMF entity communicateswith the NG-RAN device through an N2 interface, and the AMF entitycommunicates with the terminal through an N1 interface. In the foregoinginterworking architecture, the N26 interface may not exist between theMME and the AMF in some scenarios, and the N26 interface may be used incontext transfer and switching processes of the terminal. Thisapplication separately describes related possible implementations forwhether the N26 interface exists between the MME and the AMF.

It should be noted that in FIG. 1, that the terminal is UE is merelyused as an example, and names of interfaces between network elements inFIG. 1 are merely examples. In specific implementation, the interfacesmay have other names. This is not specifically limited in theembodiments of this application.

It should be noted that the NG-RAN device in the 5G network may also bereferred to as an access device. The access device is a device accessinga core network. For example, the access device may be a base station, abroadband network gateway (BNG), an aggregation switch, or a non-3GPPaccess device. The base station may include various forms of basestations, for example, a macro base station, a micro base station (alsoreferred to as a small cell), a relay node, and an access point. This isnot specifically limited in the embodiments of this application.

Certainly, the 4G network and the 5G network may further include othernetwork elements. For example, the 4G network may further include ageneral packet radio system (GPRS) serving support node (SGSN), and the5G network may further include an authentication server function (AUSF)entity and a network slice selection function (NSSF) entity. This is notspecifically limited in the embodiments of this application.

The terminal in the embodiments of this application may include varioustypes of handheld devices, in-vehicle devices, wearable devices, andcomputing devices that have a wireless communication function, oranother processing device connected to a wireless modem; or may includea subscriber unit, a cellular phone, a smart phone, a wireless datacard, a personal digital assistant (PDA) computer, a tablet computer, awireless modem, a handheld device, a laptop computer, a cordless phoneor a wireless local loop (WLL) station, a machine type communication(MTC) terminal, user equipment (UE), a mobile station, a terminaldevice, and the like. For ease of description, the devices mentionedabove are collectively referred to as the terminal in this application.

APN:

In the 4G network, the terminal may provide an APN for the MME wheninitiating a packet service. The MME parses a domain name by using adomain name server (DNS) and based on the APN provided by the terminal,so as to obtain an address (for example, an internet protocol address)of a session management network element, so that the terminal accesses aPDN corresponding to the APN.

DNN:

In the 5G network, the terminal may provide S-NSSAI and a DNN for theAMF when initiating PDU session establishment. The AMF determines anaddress of a session management network element based on the S-NSSAI,the DNN, and other information (such as subscription information of theterminal and a local operator policy). The determined session managementnetwork element establishes a PDU session for the terminal based on theS-NSSAI and the DNN.

The APN in the 4G network is equivalent to the DNN in the 5G network,and a PDN connection in the 4G network is equivalent to a PDU session inthe 5G network. The UE may establish one or more PDU sessions in 5Q andthe PDU sessions may use a same DNN. The one or more PDU sessions with asame DNN may be anchored to different control plane function networkelements. In 4G, to control an aggregate maximum bit rate (AMBR) of theAPN, it is required that one or more PDN connections with a same APN canbe anchored to only one control plane function network element. If oneor more PDU sessions with a same DNN in 5G are switched to one or morePDN connections with a same APN in 4Q how to switch a session is aproblem to be resolved urgently. Specific to this problem, in theembodiments of this application, a target PDU session may be determinedfrom at least one PDU session with a same DNN based on switchingindication information, and the target PDU session is used as a PDUsession that can be switched, so as to avoid an uncontrolled situationcaused because how to switch at least one PDU session with a same DNN isunknown, thereby improving system performance. The following details,with reference to the accompanying drawings, communication methodsprovided in the embodiments of this application.

FIG. 2 shows a communication method 200 according to an embodiment ofthis application. The method 200 includes the following steps.

S210. A network device determines, based on switching indicationinformation of protocol data unit PDU sessions established by a terminalin a first network, a target PDU session from the established PDUsessions, where all the established PDU sessions have a same datanetwork name DNN. Optionally, the terminal may establish one or more PDUsessions in the first network. Optionally, there may be one or moretarget PDU sessions. Optionally, the network device may be a user datamanagement network element or an access and mobility management functiondevice.

It should be noted that if the terminal establishes N PDU sessions inthe first network, M PDU sessions in the N PDU sessions have a same datanetwork name, where N is greater than or equal to M, and M and N arepositive integers.

It should be understood that the switching indication information of theestablished PDU sessions may include the following: Each PDU session inthe established PDU sessions may have corresponding switching indicationinformation, and PDU sessions with same or different switchingindication information may exist in the established PDU sessions.Alternatively, at least one PDU session in the established PDU sessionshas corresponding switching indication information. For example, theswitching indication information may indicate whether the PDU sessioncan be switched. For example, if only one of three PDU sessions can beswitched, there is switching indication information corresponding to thePDU session, and the switching indication information indicates that thePDU session can be switched. Whether the remaining two PDU sessions canbe switched may not be indicated, and it is considered by default thatthe remaining two PDU sessions cannot be switched.

In this embodiment of this application, the switching indicationinformation has at least two different indication functions, and twocases are described below.

Case 1: The switching indication information is used to indicate aswitching priority of each PDU session in the established PDU sessions.S220 includes the following: The network device determines, as thetarget PDU session, a PDU session with a highest switching priority inthe established PDU sessions. It should be understood that in thisembodiment of this application, the switching priority of each PDUsession may be a number representing a priority. For example, a priority1 represents a highest priority, that is, a PDU session with thispriority is preferably switched to a second network; and a priority 100represents a lowest priority. If there are currently five PDU sessions:a session 1, a session 2, a session 3, a session 4, and a session 5, andpriorities of the five PDU sessions are respectively 1, 2, 3, 4, and 5in descending order, the network device determines the session 1 as thetarget PDU session.

Case 2: The switching indication information is used to indicate whethereach PDU session in the established PDU sessions can be switched. Forexample, the switching indication information may be an indicationfield. For example, when an indication field of a PDU session is 1, itindicates that the PDU session can be switched; and when an indicationfield of a PDU session is 0, it indicates that the PDU session cannot beswitched. S220 includes the following: When the switching indicationinformation indicates that there is only one PDU session that can beswitched, the network device determines the PDU session that can beswitched as the target PDU session. In other words, there is only onePDU session that can be switched, and the PDU session is the target PDUsession. Alternatively, when the switching indication informationindicates that there are at least two PDU sessions that can be switched,the network device determines the target PDU session from the at leasttwo PDU sessions. For example, the network device may randomly selectone PDU session from the at least two PDU sessions as the target PDUsession or select one PDU session as the target PDU session based onassistance information.

Optionally, in Case 2, that when the switching indication informationindicates that there are at least two PDU sessions that can be switched,the network device determines the target PDU session from the at leasttwo PDU sessions includes the following: If the at least two PDUsessions belong to a same control plane function network element, thenetwork device determines each of the at least two sessions as thetarget PDU session, that is, the network device may determine, as thetarget PDU sessions, the at least two PDU sessions belonging to the samecontrol plane function network element, and switch the target PDUsessions to the second network. Alternatively, if the at least two PDUsessions belong to different control plane function network elements,the network device determines the target PDU session from the at leasttwo PDU sessions based on assistance information of each of the at leasttwo PDU sessions. Optionally, the network device may determine switchingpriorities of the at least two PDU sessions based on the assistanceinformation of each PDU session. The network device determines thetarget PDU session from the at least two PDU sessions based on theswitching priorities of the at least two PDU sessions.

Optionally, the assistance information includes at least one of thefollowing: an internet protocol IP address version corresponding to thePDU session, single network slice selection assistance information(S-NSSAI) corresponding to the PDU session, a session and servicecontinuity (SSC) mode corresponding to the PDU session, an allocationand retention priority (ARP) corresponding to the PDU session, a servicetype corresponding to the PDU session, and an establishment timecorresponding to the PDU session. For example, the switching indicationinformation indicates that a PDU session 1 and a PDU session 2 can beswitched. For example, if the PDU session 1 belongs to a voice serviceand the PDU session 2 belongs to a network data service, the networkdevice may determine the PDU session 1 as the target PDU session; or thenetwork device may determine that a priority of the PDU session 1 ishigher than that of the PDU session 2, and determine the session 1 asthe target PDU session when no other PDU session with a higher priorityexists. For another example, if an SSC mode of a PDU session 1 is a mode3 and an SSC mode of a PDU session 2 is a mode 2, the network device maydetermine the PDU session 1 as the target PDU session; or the networkdevice determines that a priority of the PDU session 1 is higher thanthat of the PDU session 2, and the network device may determine the PDUsession 1 as the target PDU session when no other PDU session with ahigher priority exists. For another example, if S-NSSAI to which a PDUsession 1 belongs has a higher priority during configuration and S-NSSAIto which a PDU session 2 belongs has a lower priority duringconfiguration, the network device may determine the PDU session 1 as thetarget PDU session; or the network device may determine that a priorityof the PDU session 1 is higher than that of the PDU session 2, and thenetwork device may determine the PDU session 1 as the target PDU sessionwhen no other PDU session with a higher priority exists. For anotherexample, when an SSC mode corresponding to a PDU session is an SSC mode3, the network device determines, based on a session establishment time,a subsequently established PDU session as the target PDU session; or thenetwork device sets a priority of a subsequently established PDU sessionto be higher than that of a previously established PDU session, anddetermines the subsequently established PDU session with a higherpriority as the target PDU session. For another example, the networkdevice may determine the target PDU session according to a locallyconfigured policy and based on an IP address version corresponding tothe PDU session, for example, determine a PDU session whose IP addressversion is v6 as the target PDU session; or the network device may set apriority of a PDU session according to a locally configured policy andbased on an IP address version corresponding to the PDU session, forexample, the locally configured policy is preferably switching a PDUsession whose IP version is v6. For another example, the network devicemay determine a priority of a PDU session based on a service type of thePDU session, and determine a PDU session whose service type is voice asthe target PDU session, or set a higher priority for a PDU session whoseservice type is voice.

It should be understood that the foregoing two cases are merely examplesfor description. In actual application, the switching indicationinformation may have another indication function. This is not limited inthis embodiment of this application.

In an optional embodiment, before S210, the method further includes thefollowing: The network device obtains the switching indicationinformation of the PDU sessions established by the terminal in the firstnetwork, and all the established PDU sessions have a same data networkname.

The network device may obtain, in the following several manners, theswitching indication information of the PDU sessions established by theterminal in the first network.

Manner 1: The network device receives the switching indicationinformation that is of the PDU sessions established by the terminal inthe first network and that is sent by at least one control planefunction network element. To be specific, each of the at least onecontrol plane function network element can obtain switching indicationinformation of a PDU session corresponding to each control planefunction network element. For example, each control plane functionnetwork element may obtain switching indication information that is of acorresponding PDU session and that is sent by the terminal, and eachcontrol plane function network element may send, to the network device,switching indication information that is of the corresponding PDUsession and that is determined by the control plane function networkelement. Alternatively, each control plane function network element mayadjust switching indication information that is of a corresponding PDUsession and that is sent by the terminal to obtain adjusted switchingindication information of the PDU session, and then send the adjustedswitching indication information of the PDU session to the networkdevice. For example, the network device may be an access and mobilitymanagement function device or a user data management network element. Inthis way, the access and mobility management function device candetermine the target PDU session from the established PDU sessions basedon the switching indication information of the established PDU sessions,or the user data management network element can determine the target PDUsession from the established PDU sessions based on the switchingindication information of the established PDU sessions.

Manner 2: The network device is a user data management network element,for example, may be the foregoing HSS+UDM; or may be an access andmobility management function device. The network device receivesassistance information that is of a first PDU session in the establishedPDU sessions and that is sent by a first control plane function networkelement, and the network device determines switching indicationinformation of the first PDU session based on the assistanceinformation. The assistance information may be the foregoing assistanceinformation. Herein, an example in which the switching indicationinformation indicates a switching priority of a PDU session is used fordescription. For example, the network device may determine a higherpriority for a corresponding PDU session with a higher S-NSSAI priority,and determine a lower priority for a corresponding PDU session with alower S-NSSAI priority. For another example, when an SSC modecorresponding to a PDU session is an SSC mode 3, the network devicesets, based on a session establishment time, a priority of asubsequently established PDU session to be higher than that of apreviously established PDU session. For another example, the networkdevice may set a priority of a PDU session according to a locallyconfigured policy and based on an IP address version corresponding tothe session. For example, the locally configured policy is preferablyswitching a PDU session whose IP version is v6. For another example, thenetwork device may determine a priority of a first PDU session based ona service type of the first PDU session, and set a higher priority for aPDU session whose service type is voice.

In Manner 2, the method further includes the following: When the networkdevice is a user data management network element, the user datamanagement network element sends the switching indication information ofthe first PDU session to the first control plane function networkelement. Optionally, the first control plane function network elementmay send the switching indication information of the first PDU sessionto the terminal.

Manner 3: The network device is a user data management network element,for example, may be the foregoing HSS+UDM. The user data managementnetwork element receives initial switching indication information thatis of a second PDU session in the established PDU sessions and that issent by a second control plane function network element. The user datamanagement network element adjusts the initial switching indicationinformation to obtain switching indication information of the second PDUsession, that is, the user data management network element may adjustthe initial switching indication information that is of the second PDUsession and that is sent by the second control plane function networkelement. For example, the user data management network element hasstored switching indication information that is of a PDU session 1 andthat is sent by a control plane function network element 1. Whenreceiving switching indication information (initial switching indicationinformation) that is of a PDU session 2 (the second PDU session) andthat is sent by a control plane function network element 2 (the secondcontrol plane function network element), the user data managementnetwork element finds that the switching indication information of thePDU session 1 is the same as that of the PDU session 2, and that the PDUsession 1 and the PDU session 2 have a same data network name. When thePDU session 1 and the PDU session 2 belong to different user planefunction network elements, the user data management network element mayadjust the switching indication information of the PDU session 2 to bedifferent from the switching indication information of the PDU session1, for example, adjust the switching indication information of the PDUsession 2 based on at least one of subscription data of the PDU session1 and the PDU session 2, identifiers of control plane function networkelements corresponding to the PDU session 1 and the PDU session 2, and alocal policy. The local policy may be a policy preset by the user datamanagement network element, or may be a policy obtained based onhistorical data. For another example, the network device adjusts theswitching indication information of the PDU session 2 based on theforegoing assistance information. This is not limited in this embodimentof this application.

In Manner 3, the method further includes the following: The user datamanagement network element sends the switching indication information ofthe second PDU session to the second control plane function networkelement. To be specific, the user data management network element sends,to the second control plane function network element, the switchingindication information that is of the second PDU session and that isobtained through adjustment. Optionally, the second control planefunction network element may send the switching indication informationof the second PDU session to the terminal. Optionally, the secondcontrol plane function network element may send the switching indicationinformation of the second PDU session to an access and mobilitymanagement function device.

Manner 4: The network device is a user data management network element.For example, the network device may be the foregoing HSS+UDM. In thiscase, the user data management network element may determine switchingindication information of each of the established PDU sessions. To bespecific, the user data management network element may determine theswitching indication information of each PDU session based onsubscription data of the PDU session and according to a local policy.For example, the local policy may be the switching indicationinformation of each PDU session that is determined based on theassistance information.

It should be understood that an obtaining manner in which the networkdevice obtains the switching indication information of each PDU sessionfrom the switching indication information of the established PDUsessions may be one of the foregoing four manners. Optionally, theswitching indication information of all the PDU sessions is obtained ina same manner. Alternatively, if there are multiple established PDUsessions, switching indication information of at least two of themultiple PDU sessions may be obtained in different manners, for example,in two of the foregoing four manners.

S220. The network device sends session information of the target PDUsession to a mobility management entity device in the second network, sothat the mobility management entity device in the second networkdetermines the session information of the target PDU session based onthe session information of the target PDU session.

Optionally, the session information of the target PDU session includesan identifier of a control plane function network element correspondingto the target PDU session and a data network name of the target PDUsession. In this way, the mobility management entity device in thesecond network can determine, based on the identifier of the controlplane function network element corresponding to the target PDU session,the control plane function network element corresponding to the targetPDU session. The mobility management entity device in the second networktransparently transmits, to the control plane function network elementcorresponding to the target PDU session, the identifier that is of thetarget PDU session and that is sent by the terminal. The control planefunction network element corresponding to the target PDU sessionsearches for the target PDU session based on the identifier of thetarget PDU session, and selects the target PDU session for switching ifthe target PDU session is found.

Optionally, the first network may be a 5G network, and the secondnetwork may be a 4G network.

Optionally, the network device may be an access and mobility managementfunction entity, for example, may be the foregoing AMF in FIG. 1.Optionally, the network device may be a user data management networkelement, for example, may be the foregoing HSS+UDM in FIG. 1. A specifictype of the network device is not limited in this embodiment of thisapplication.

Optionally, in this embodiment of this application, the target PDUsession is used as a PDU session to be switched to the second network,and a PDU session other than the target PDU session in the PDU sessionsestablished by the terminal in the first network may be released.

Therefore, according to the communication method provided in thisembodiment of this application, the network device may determine, basedon the switching indication information, the target PDU session from thePDU sessions established by the terminal in the first network. In thisway, the target PDU session may be used as a PDU session that can beswitched to the second network, so as to avoid an uncontrolled situationcaused when all the PDU sessions established by the terminal in thefirst network need to be switched to a same control plane functionnetwork element in the second network. This helps control switching of aPDU session, thereby improving system performance.

FIG. 3 shows a communication method 300 according to an embodiment ofthis application. The method 300 includes the following steps.

S310. A terminal obtains switching indication information of protocoldata unit PDU sessions established in a first network, where all theestablished PDU sessions have a same data network name DNN. Optionally,there may be one or more PDU sessions established in the first network.

It should be understood that the switching indication information of theestablished PDU sessions may include the following: There may becorresponding switching indication information for each of theestablished PDU sessions, and PDU sessions corresponding to same ordifferent switching indication information may exist in the establishedPDU sessions. Alternatively, there is switching indication informationcorresponding to at least one PDU session in the established PDUsessions. For example, the switching indication information may indicatewhether the PDU session can be switched. For example, if only one ofthree PDU sessions can be switched, there is switching indicationinformation corresponding to the PDU session, and the switchingindication information indicates that the PDU session can be switched.Whether the remaining two PDU sessions can be switched may not beindicated, and it is considered by default that the remaining two PDUsessions cannot be switched.

The terminal may obtain, in the following three manners, the switchingindication information of the PDU sessions established in the firstnetwork.

Manner 1: The terminal determines the switching indication informationof the established PDU sessions. For example, the terminal determinesswitching indication information of at least one PDU session accordingto a local policy. In the local policy, the switching indicationinformation of the established PDU sessions may be determined based onS-NSSAI of PDU sessions with a same DNN. For example, if specificS-NSSAI has a relatively high priority in a configuration process, a PDUsession corresponding to the S-NSSAI has a highest priority; orswitching indication information of a PDU session may be determinedbased on a service type carried by the PDU session; or switchingindication information of a PDU session is determined based on acombination of the S-NSSAI and the service type. For example, theswitching indication information indicates a switching priority. Whenthe terminal determines, based on S-NSSAI, switching priorities of thePDU sessions established in the first network, the terminal mayconfigure a correspondence between S-NSSAI and a switching priority, asdescribed in Table 1; and the terminal may configure a correspondencebetween a service type and a switching priority, as described in Table2.

TABLE 1 S-NSSAI 1 Priority = 1 S-NSSAI 2 Priority = 2 S-NSSAI 3 Priority= 3 S-NSSAI 4 Priority = 4

TABLE 2 Signaling Priority = 1 Voice Priority = 2 Internet of things(Internet od things, IoT) Priority = 3 Internet (Internet) Priority = 4

It should be understood that when the switching indication informationindicates a switching priority, the terminal may not change switchingindication information of a previously established PDU session whendetermining switching indication information of a subsequentlyestablished PDU session. For example, the terminal determines theswitching indication information of the PDU session according to adetermined rule.

When the switching indication information indicates whether a PDUsession can be switched, the terminal determines whether the PDU sessioncan be switched. The terminal may determine, based on S-NSSAIcorresponding to the PDU session, that the PDU session can be switched.In this case, the terminal changes switching indication information of apreviously established PDU session when determining switching indicationinformation of a subsequently established PDU session. As described inTable 1, the terminal first establishes a PDU session in a network slicecorresponding to the S-NSSAI 4. The PDU session is the first PDU sessioncorresponding to the DNN, and the terminal determines that the PDUsession can be switched. Afterwards, the terminal establishes a new PDUsession in a network slice corresponding to the S-NSSAI 1. Because apriority of the S-NSSAI 1 is higher than that of the S-NSSAI 4, theterminal sets the PDU session in the network slice corresponding to theS-NSSAI 1 to be switchable, and sets the PDU session previouslyestablished in the network slice corresponding to the S-NSSAI 4 to benon-switchable. For example, when establishing a new PDU session in anSSC mode 2, the terminal sets the new PDU session to be switchable, andsets a PDU session, in the SSC mode 2, with a same DNN as the new PDUsession to be non-switchable. Optionally, each time the terminaldetermines switching indication information of a PDU session, theterminal may send the switching indication information of the PDUsession to a corresponding control plane function network element.

It should be understood that when switching indication information of anewly established PDU session affects switching indication informationof an established PDU session, for example, the newly established PDUsession is determined by the terminal as “switchable”, and consequentlythe previously established PDU session with a same DNN as the newlyestablished PDU session is determined as “non-switchable”, the terminalsends the switching indication information of the newly established PDUsession to a control plane function network element, and the controlplane function network element sends the switching indicationinformation of the newly established PDU session to an HSS+UDM. Whenreceiving the switching indication information of the PDU session, theHSS+UDM sets the switching indication information of the PDU sessionthat has a same DNN as the PDU session and that is previously determinedas “switchable” to be non-switchable, and notifies a control planefunction network element corresponding to the PDU session of thissetting.

Manner 2: The terminal receives the switching indication information ofthe established PDU sessions that is sent by at least one control planefunction network element. The at least one control plane functionnetwork element may send, to the terminal, switching indicationinformation that is of a corresponding PDU session and that isdetermined by the at least one control plane function network element.For example, the control plane function network element determines theswitching indication information of the PDU session based on assistanceinformation of the PDU session, and sends the determined switchingindication information of the PDU session to the terminal. For aspecific method for determining the switching indication information ofthe PDU session based on the assistance information of the PDU session,refer to the description in the method 200. Alternatively, each of theat least one control plane function network element may obtain switchingindication information that is of a PDU session corresponding to thecontrol plane function network element and that is sent by a user datamanagement network element, and send the switching indicationinformation of the PDU session to the terminal. How each of the at leastone control plane function network element obtains the switchingindication information of the PDU session corresponding to the controlplane function network element is not limited in this embodiment of thisapplication.

Manner 3: The terminal sends initial switching indication information ofthe first PDU session to a second control plane function networkelement, where the initial switching indication information is used todetermine switching indication information of the first PDU session. Theterminal receives switching priority information that is of the firstPDU session and that is sent by the second control plane functionnetwork element. To be specific, the terminal sends, to the secondcontrol plane function network element, the initial switching indicationinformation that is of the first PDU session and that is determined bythe terminal, and the second control plane function network element mayadjust the initial switching indication information that is of the firstPDU session and that is sent by the terminal. For example, the secondcontrol plane function network element has determined switchingindication information of a PDU session 1. When the second control planefunction network element receives switching indication information thatis of a PDU session 2 (the first PDU session) and that is sent by theterminal, the second control plane function network element determinesthat the PDU session 1 and the PDU session 2 belong to a same secondcontrol plane function network element and a same user plane functionnetwork element, and the second control plane function network elementfinds that the switching indication information of the PDU session 1 isdifferent from that of the PDU session 2, the second control planefunction network element adjusts initial switching indicationinformation of the PDU session 2 to the switching indication informationof the PDU session 1. That is, the second control plane function networkelement may adjust, based on switching indication information that is ofa PDU session and that is sent by the terminal and switching indicationinformation that is of a PDU session and that is stored by the secondcontrol plane function network element, the switching indicationinformation that is of the PDU session and that is sent by the terminal.For another example, the second control plane function network elementhas determined switching indication information of a PDU session 1. Whenthe second control plane function network element receives switchingindication information that is of a PDU session 2 and that is sent bythe terminal, and the switching indication information of the PDUsession 1 is the same as that of the PDU session 2 but user planefunction network elements of the PDU session 1 and the PDU session 2 aredifferent, the second control plane function network element adjusts theswitching indication information of the PDU session 2 to be differentfrom the switching indication information of the PDU session 1. Forexample, when the switching indication information is used to indicate apriority of a PDU session, the second control plane function networkelement may adjust a priority of the PDU session 2 to be lower or higherthan that of the PDU session 1. The foregoing is only an example fordescribing the following: The second control plane function networkelement has a function of adjusting switching indication information ofa PDU session. Specifically, an adjustment manner and an adjustmentpolicy are not limited in this embodiment of this application.

It should be understood that if the terminal determines the first PDUsession as a target PDU session, a first control plane function networkelement is the second control plane function network element.

S320. The terminal determines the target PDU session from theestablished PDU sessions based on the switching indication information.Optionally, there may be one or more target PDU sessions. This is notlimited in this embodiment of the present invention.

In this embodiment of this application, the switching indicationinformation has at least two different indication functions, and twocases are described below.

Case 1: The switching indication information is used to indicate aswitching priority of each of the established PDU sessions, and S320includes the following: The terminal determines, as the target PDUsession, a PDU session with a highest switching priority in theestablished PDU sessions. For example, if there is one PDU session witha highest switching priority, the one PDU session is the target PDUsession; or if there are at least two PDU sessions with a highestswitching priority, the at least two PDU sessions are target PDUsessions. Specifically, for a concept of the switching priority, referto the description in the method 200.

Case 2: The switching indication information is used to indicate whethereach of the established PDU sessions can be switched. For example, theswitching indication information may be an indication field. Forexample, when an indication field of a PDU session is 1, it indicatesthat the PDU session can be switched; and when an indication field of aPDU session is 0, it indicates that the PDU session cannot be switched.S320 includes the following: The terminal determines, as the target PDUsession, a PDU session indicated by the switching indication informationas “switchable”. To be specific, if the switching indication informationindicates that there is one PDU session that can be switched, the PDUsession is the target PDU session; or if the switching indicationinformation indicates that there are multiple PDU sessions that can beswitched, all the multiple PDU sessions can be target PDU sessions. Theplurality of target PDU sessions may be corresponding to a same controlplane function network element and a same user plane function networkelement. For example, the control plane function network element may bean SMF+PGW-C, and the user plane function network element may be aUPF+PGW-U.

S330. The terminal sends an identifier of the target PDU session to thefirst control plane function network element by using a mobilitymanagement entity device in a second network.

In an optional embodiment, S330 includes the following: The terminalsends the identifier of the target PDU session and a DNN of the targetPDU session to the mobility management entity device. The DNN of thetarget PDU session is used by the mobility management entity device todetermine the first control plane function network element, so that themobility management entity device sends the identifier of the target PDUsession to the first control plane function network element. In otherwords, the terminal may send the identifier of the target PDU sessionand the data network name of the target PDU session to the mobilitymanagement entity device in the second network. The mobility managemententity device in the second network may determine, based on the datanetwork name of the target PDU session, the first control plane functionnetwork element corresponding to the target PDU session. Specifically,the user data management network element may send, to the mobilitymanagement entity device in the second network, an identifier of acontrol plane function network element corresponding to each datanetwork name. After receiving the identifier that is of the controlplane function network element corresponding to each data network nameand that is sent by the user management network element, the mobilitymanagement entity device in the second network searches, based on thedata network name that is of the target PDU session and that is sent bythe terminal, for the first control plane function network elementcorresponding to the determined target PDU session. The mobilitymanagement entity device in the second network may send the identifierof the target PDU session to the first control plane function networkelement. In this way, the first control plane function network elementcan determine, based on the identifier of the target PDU session, a PDUsession that needs to be switched. For example, the mobility managemententity device in the second network may be an MME. For example, theterminal sends the ID of the target PDU session and a DNN 1 of thetarget PDU session to the mobility management entity device in thesecond network. The user management network element determines a targetPDU session (a PDU session with a highest priority or a PDU session thatcan be switched) corresponding to each DNN; sends, to the mobilitymanagement entity in the second network, the DNN 1 and a control planefunction network element 1 corresponding to the DNN 1 (a PDU sessioncorresponding to the control plane function network element 1 is atarget PDU session, and a data network name of the target PDU session isthe DNN 1); and also sends, to the mobility management entity device, aDNN 2 and a control plane function network element 2 corresponding tothe DNN 2 (a PDU session corresponding to the control plane functionnetwork element 2 is a target PDU session, and a data network name ofthe target PDU session is the DNN 2). The mobility management in thesecond network may determine that the DNN 1 is corresponding to thecontrol plane function network element 1, and therefore the mobilitymanagement entity device in the second network may send the identifierof the target PDU session to the control plane function network element1 (the first control plane function network element). In this way, thecontrol plane function network element 1 may determine the target PDUsession that needs to be switched.

In an optional embodiment, that the terminal sends the identifier of thetarget PDU session and a data network name of the target PDU session tothe mobility management entity device includes the following: Theterminal sends a first request message to the mobility management entitydevice. The first request message carries the identifier of the targetPDU session and the data network name of the target PDU session, and thefirst request message is an attach request message or a sessionestablishment request message. To be specific, after determining thetarget PDU session, the terminal may add the identifier of the targetPDU session and the data network name of the target PDU session to theattach request message when sending the attach request message to themobility management entity device in the second network, or may add theidentifier of the target PDU session and the data network name of thetarget PDU session to the session establishment request message. Amanner in which the terminal sends the identifier of the target PDUsession and the data network name of the target PDU session to themobility management entity device in the second network is not limitedin this embodiment of this application.

FIG. 4 shows a communication method 400 according to an embodiment ofthis application. The method 400 includes the following steps.

S410. A terminal sends a first data network name corresponding to acurrent PDU session to a mobility management entity device in a secondnetwork, so that the mobility management entity device in the secondnetwork can determine a control plane function network elementcorresponding to the current PDU session. For a specific determiningmanner, refer to the method 300. The mobility management entity devicein the second network may send, to the control plane function networkelement, a PDU session (the current PDU session) update requestcorresponding to a first data network name. After receiving the sessionupdate request corresponding to the first data network name, the controlplane function network element obtains, based on the first data networkname, a PDU session corresponding to the first data network name. If thefirst data network name is corresponding to one PDU session, the PDUsession is a session that needs to be switched; or if the first datanetwork name is corresponding to multiple PDU sessions, the controlplane function network element selects one PDU session as a PDU sessionthat needs to be switched. The control plane function network elementmay randomly select one PDU session as a PDU session that needs to beswitched; or determine, based on assistance information of a PDUsession, a PDU session that needs to be switched, for example,determine, based on S-NSSAI corresponding to a session, a PDU sessionthat needs to be switched. Alternatively, if an SSC mode of a PDUsession is 3, the control plane function network element determines,based on a time at which a PDU session is established, a PDU sessionthat needs to be switched. Alternatively, the control plane functionnetwork element determines, based on an IP address version of a PDUsession, a PDU session that needs to be switched. Alternatively,optionally, the control plane function network element may search a userdata management network element for a session identifier of a PDUsession that needs to be switched; and determine, based on the sessionidentifier of the PDU session that needs to be switched, the PDU sessionthat needs to be switched. This is not limited in this embodiment ofthis application.

Optionally, S410 may include the following: The terminal sends an attachrequest message or a session establishment request message to themobility management entity device in the second network. The attachrequest message or the session establishment request message carries thefirst data network name corresponding to the current PDU session.

Optionally, if the terminal sends, in the attach request message, thefirst data network name corresponding to the current PDU session to themobility management entity device in the second network, afterdetermining a PDU session that needs to be switched, the control planefunction network element switches the PDU session to a PDN connection inan attach procedure. Alternatively, if the terminal adds, to the sessionestablishment request message, the data network name corresponding tothe current PDU session, after determining a PDU session that needs tobe switched, the control plane function network element switches the PDUsession to a PDN connection in a session establishment requestprocedure. After completing switching, the control plane functionnetwork element sends the identifier of the switched PDU session to theterminal. For example, the control plane function network element sendsa protocol configuration option (PCO) to the terminal, and the PCOcarries the identifier of the switched PDU session.

S420. The terminal receives the identifier that is of the switched PDUsession and that is sent by the control plane function network element,and determines the switched PDU session based on the identifier of thePDU session. Optionally, the terminal receives the PCO sent by thecontrol plane function network element, obtains the identifier of theswitched PDU session from the PCO, and determines the switched PDUsession based on the identifier of the PDU session. In this way, UE canassociate a PDN connection with a corresponding session.

FIG. 5 shows a communication method 500 according to an embodiment ofthis application. The method 500 includes the following steps.

S510. A first control plane function network element receives a sessionestablishment request message sent by a terminal, where the sessionestablishment request message is used to request to establish a firstprotocol data unit PDU session.

S520. The first control plane function network element obtains switchingindication information of the first PDU session. Optionally, theswitching indication information is used to indicate a priority of thefirst PDU session or used to indicate whether the first PDU session canbe switched. The first control plane function network element obtainsfirst switching indication information of the first PDU session in thefollowing five manners.

Manner 1: The session establishment request message in S510 carries theswitching indication information of the first PDU session. The firstcontrol plane function network element may determine the switchingindication information of the first PDU session from the sessionestablishment request message.

In Manner 1, after obtaining the switching indication information of thefirst PDU session, the first control plane function network element maysend the switching indication information of the first PDU session to auser data management network element. After the user data managementnetwork element receives switching indication information that iscorresponding to each of multiple PDU sessions (the multiple PDUsessions have a same DNN) and that is sent by multiple control planefunction network elements, the user data management network element canstore the switching indication information corresponding to each PDUsession; and when the terminal is handed over to a second network,determine a target PDU session based on the switching indicationinformation corresponding to each of the multiple PDU sessions, that is,determine a PDU session that can be switched. Alternatively, the firstcontrol plane function network element may send the switching indicationinformation of the first PDU session to an access and mobilitymanagement function device. After the access and mobility managementfunction device receives switching indication information that iscorresponding to each of multiple PDU sessions (the multiple PDUsessions have a same DNN) and that is sent by multiple control planefunction network elements, the access and mobility management functiondevice can store the switching indication information corresponding toeach PDU session; and when the terminal is handed over, determine atarget PDU session based on the switching indication informationcorresponding to each of the multiple PDU sessions, that is, determine aPDU session that can be switched.

Optionally, the first control plane function network element may send aDNN of the first PDU session and an identifier of the first controlplane function network element to the user data management networkelement. The first control plane function network element may sendsession information of the first PDU session to the user data managementnetwork element, where the session information includes the switchingindication information of the first PDU session, the DNN of the firstPDU session, and the identifier of the first control plane functionnetwork element. In this way, the user data management network elementcan store the session information of the first PDU session. Whenreceiving session information of multiple PDU sessions (the multiple PDUsessions have a same DNN), the user data management network elementdetermines a target PDU session based on switching indicationinformation of the multiple PDU sessions, and then sends, to a mobilitymanagement function entity device in the second network, a DNN of thetarget PDU session and an identifier of a control plane function networkelement corresponding to the target PDU session.

Manner 2: The first control plane function network element receivesinitial switching indication information that is of the first PDUsession and that is sent by the terminal. The first control planefunction network element obtains the switching indication informationthat is of the first PDU session and that is obtained through adjustmentbased on the initial switching indication information.

In Manner 2, the first control plane function network element sends theswitching indication information of the first PDU session to theterminal, a user data management network element, or an access andmobility management function.

Manner 3: The first control plane function network element receivesinitial switching indication information that is of the first PDUsession and that is sent by the terminal. The first control planefunction network element sends the initial switching indicationinformation of the first PDU session to a user data management networkelement. The user data management network element adjusts the initialswitching indication information of the first PDU session to obtain theswitching indication information of the first PDU session. The user datamanagement network element sends the switching indication information ofthe first PDU session to the first control plane function networkelement.

In Manner 3, the first control plane function network element sends thefirst switching indication information to the terminal or an access andmobility management function, that is, the first control plane functionnetwork element sends the adjusted switching indication information ofthe first PDU session to the terminal.

Manner 4: The first control plane function network element sendsassistance information of the first PDU session to a user datamanagement network element. The user data management network elementdetermines the switching indication information of the first PDU sessionbased on the assistance information of the first PDU session, and thensends the switching indication information of the first PDU session tothe first control plane function network element. The first controlplane function network element receives the switching indicationinformation that is of the first PDU session and that is sent by theuser data management network element. The assistance information of thefirst PDU session includes at least one of an internet protocol IPaddress version corresponding to the first PDU session, single networkslice selection assistance information corresponding to the first PDUsession, a session and service continuity SSC mode corresponding to thefirst PDU session, an allocation and retention priority ARPcorresponding to the first PDU session, a service type corresponding tothe first PDU session, and an establishment time corresponding to thefirst PDU session.

In Manner 4, the method further includes the following: The firstcontrol plane function network element sends the first switchingindication information of the first PDU session to the terminal or anaccess and mobility management function.

Manner 5: The first control plane function network element determinessecond switching indication information of the first PDU sessionaccording to a local policy. The first control plane function networkelement sends the second switching indication information to a user datamanagement network element. The user data management network elementadjusts the second switching indication information to obtain the firstswitching indication information of the first PDU session, and sends thefirst switching indication information to the first control planefunction network element.

In the foregoing five manners, when the first control plane functionnetwork element sends the switching indication information of the firstPDU session to the terminal, the terminal may receive switchingindication information of multiple PDU sessions (the multiple PDUsessions have a same DNN) that is sent by multiple control planefunction network elements, the terminal may determine a target PDUsession from the multiple PDU sessions based on the switching indicationinformation of the multiple PDU sessions, and the terminal may send anidentifier of the target PDU session and a DNN of the target PDU sessionto the mobility management function entity device. Alternatively, thefirst control plane function network element sends the switchingindication information of the first PDU session to the user datamanagement network element. Optionally, the first control plane functionnetwork element may send the DNN of the first PDU session and theidentifier of the first control plane function network element to theuser data management network element. The user data management networkelement may receive switching indication information of multiple PDUsessions (the multiple PDU sessions have a same DNN) that is sent bymultiple control plane function network elements, and the user datamanagement network element may determine a target PDU session from themultiple PDU sessions based on the switching indication information ofthe multiple PDU sessions. The user data management network elementsends, to the mobility management function entity device, a DNN of thetarget PDU session and an identifier of a control plane function networkelement corresponding to the target PDU session. Alternatively, thefirst control plane function network element sends the switchingindication information of the first PDU session to an access andmobility management function. Optionally, the first control planefunction network element may send the DNN of the first PDU session andthe identifier of the first control plane function network element tothe access and mobility management function. The access and mobilitymanagement function may receive switching indication information ofmultiple PDU sessions (the multiple PDU sessions have a same DNN) thatis sent by multiple control plane function network elements, and theaccess and mobility management function may determine a target PDUsession from the multiple PDU sessions based on the switching indicationinformation of the multiple PDU sessions. The access and mobilitymanagement function sends, to the mobility management function entitydevice in the second network, a DNN of the target PDU session and anidentifier of a control plane function network element corresponding tothe target PDU session.

It should be understood that in the embodiments of this application, asame term may be used in the method 200 to the method 500. However, thesame term may express different meanings in different methods. Forexample, the first control plane function network element may be anycontrol plane function network element, and does not represent a samedevice in the method 200 to the method 500. To be specific, in theembodiments of this application, “first” or “second” does not indicate aspecific one, but indicate a general one.

The following details, with reference to the accompanying drawings,communication methods provided in the embodiments of this application.In a method 600 to a method 900, an example is used for description inwhich a terminal is UE, an access and mobility management functiondevice is an AMF, a mobility management entity device is an MME, acontrol plane function network element is an SMF+PGW-C, a user datamanagement network element is an HSS+UDM, a first network is a 5Gnetwork, a second network is a 4G network, and switching indicationinformation indicates a switching priority. However, this is not limitedin the embodiments of this application.

The following separately provides descriptions for whether an N26interface exists between the MME and the AMF. In the followingdescriptions, the switching indication information may indicate aswitching priority. When the terminal is handed over from a 5G system toan evolved packet system (evolved packet system, EPS), the terminaldetermines, based on switching indication information corresponding toPDU sessions with a same DNN, a PDU session to be switched to the EPS.In an implementation, to select a target PDU session, the UE sends aswitching priority to the SMF+PGW-C, and the SMF+PGW-C may determine afinal switching priority and send the final switching priority back tothe UE. If one SMF+PGW-C and one UPF+PGW-U serve multiple PDU sessionswith a same DNN, the SMF+PGW-C may set priorities of the multiple PDUsessions to a same value.

In a scenario in which the N26 interface is not deployed, the SMF+PGW-Csends a switching priority, a DNN, and an SMF+PGW-C ID to the HSS+UDM.When the UE moves to the EPS, the UE selects a PDU session with ahighest switching priority, sends a PDN connection establishment requestmessage to the MME, and adds an ID of the PDU session to a PCO. For aDNN, the HSS+UDM sends an ID of an SMF+PGW-C with a highest switchingpriority to the MME, so as to switch the PDU session with a highestswitching priority to a corresponding PDN connection in the EPS.

In a scenario in which the N26 interface is deployed, the SMF+PGW-Csends a switching priority and a session context to the AMF together.The AMF selects a PDU session with a highest switching priority, andforwards a context of the PDU session to the MME. In this way, the PDUsession with a highest switching priority is correspondingly switched tothe EPS.

In this way, the solution has no impact on the MME, and has littleimpact on the HSS+UDM. With this solution, PDU sessions with a same DNNthat are served by a same SMF+PGW-C and a same UPF+PGW-U may be switchedto the EPS. Such selection can reflect a user requirement. In thissolution, the UE may determine a switching priority when establishing aPDU session, for example, determine the switching priority according tothe manner in the method 300. The switching priority may be determinedby the UE, or the switching priority may be determined by the SMF+PGW-Cand/or the HSS+UDM. When a PDU session is being established, theSMF+PGW-C may first determine whether the PDU session can be switched tothe 4G network. For example, when a PDU session is in an SSC mode 2, theSMF+PGW-C may determine that the PDU session does not need to beswitched to the 4G network. When the SMF+PGW-C registers an SMF+PGW-C IDand a DNN with the HSS+UDM, the SMF+PGW-C may indicate whether a PDUsession can be switched to the 4G network. In addition, the SMF+PGW-Cmay send other assistance information to the HSS+UDM, for example,S-NSSAI, an IP address version, an SSC mode, an ARP, a service type, andan establishment time that are of a PDU session, so that the HSS+UDMdetermines a switching priority based on the assistance information.

When the HSS+UDM receives registration of a PDU session, if multiple PDUsessions with a same DNN can be switched to the 4G network, the HSS+UDMdetermines switching priorities of the multiple PDU sessions based onswitching assistance information. For example, for PDU sessions with asame DNN in an SSC mode 3, the HSS+UDM may mark a latest PDU sessionwith a higher priority. For different IP versions, the HSS+UDM mayconfigure a default policy to select a PDU session, and the like.

In the scenario in which the N26 interface is not deployed, when the UEmoves to the EPS, the UE adds only a DNN to the PDN connectionestablishment request message sent to the MME, and the UE does notselect a to-be-switched PDU session. Therefore, the UE does not add anID of the PDU session to the PCO. For a DNN, the HSS+UDM may send, tothe MME, an ID of an SMF+PGW-C corresponding to a PDU session with ahighest priority. After PDN connection establishment is completed in theEPS, the SMF+PGW-C may indicate, to the terminal by using the PCO, an IDof an established PDU session with the DNN, so that the UE can associatea PDN connection with a corresponding session. In the scenario in whichN26 is deployed, the AMF may determine a session that can be switched to4Q and a processing manner is similar to that used by the HSS+UDM.

In the following figures, FIG. 6A to FIG. 9 show scenarios in which theN26 interface is not deployed, and FIG. 10A to FIG. 13 show scenarios inwhich the N26 interface is deployed.

FIG. 6A, FIG. 6B, and FIG. 6C show a communication method 600 accordingto an embodiment of this application. The method 600 includes thefollowing steps.

S601. UE determines switching indication information of PDU sessionswhen establishing the PDU sessions in a 5G network, where all theestablished PDU sessions have a same DNN. The switching indicationinformation of the PDU session indicates a switching priority orindicates whether the PDU session can be switched. For a method fordetermining the switching indication information of the PDU session bythe UE, refer to the method 300.

S602. The UE adds the switching indication information of theestablished PDU session to a session establishment request message andsends the session establishment request message to an AMF; or thesession establishment request message includes a PCO, and the UE may addthe switching indication information of the established PDU session tothe PCO. After determining switching indication information of each PDUsession, the UE may send the switching indication information of the PDUsession to the AMF by using the session establishment request message.

S603. The AMF receives the session establishment request message sent bythe UE, without parsing out the switching indication information, of thePDU session, included in the session establishment request message, andthe AMF directly forwards the switching indication information of thePDU session to an SMF+PGW-C by using a non-access stratum (NAS) message.In other words, one session establishment request message carries onePCO, and the PCO includes switching indication information of a PDUsession. For ease of description, only one SMF+PGW-C is shown in FIG.6A, FIG. 6B, and FIG. 6C. In an actual application process, there may bemultiple SMF+PGW-Cs. To be specific, the AMF sends, to each SMF+PGW-C,switching indication information of a PDU session corresponding to theSMF+PGW-C.

S604. The SMF+PGW-C receives the non-access stratum message sent by theAMF, and obtains the switching indication information of the PDU sessionfrom the non-access stratum message. Optionally, the SMF+PGW-C mayadjust the received switching indication information of the PDU session,and determine final switching indication information of the PDU session.For example, the SMF+PGW-C receives switching indication information ofa PDU session 1 and a PDU session 2 that is sent by the terminal, theswitching indication information of the PDU session 1 and the switchingindication information of the PDU session 2 that are sent by theterminal are different, and UPF+PGW-Us of the PDU session 1 and the PDUsession 2 are the same. In this case, the SMF+PGW-C may adjust theswitching indication information of the PDU session 1 and the switchingindication information of the PDU session 2 to be the same. For anotherexample, switching indication information of a PDU session 1 andswitching indication information of a PDU session 2 that are sent by theterminal are the same, and UPF+PGW-Us of the PDU session 1 and the PDUsession 2 are different. In this case, the SMF+PGW-C may adjust theswitching indication information of the PDU session 1 and the switchingindication information of the PDU session 2 to be different.

S605. When the SMF+PGW-C does not adjust the switching indicationinformation of the PDU session, the SMF+PGW-C directly sends receivedsession information of the PDU session to an HSS+UDM. The sessioninformation of the PDU session includes the switching indicationinformation of the PDU session, an identifier of the SMF+PGW-C, and aDNN of the PDU session. For example, the identifier of the SMF+PGW-C maybe an SMF+PGW-C ID. After adjusting the switching indication informationof the PDU session, the SMF+PGW-C sends adjusted switching indicationinformation, the identifier of the SMF+PGW-C, and the DNN of the PDUsession to the HSS+UDM. It should be understood that the DNN herein maybe learned of by the SMF+PGW-C or sent by the terminal to the SMF+PGW-C.This is not limited in this embodiment of this application.

S606. After receiving the session information that is of the PDU sessionestablished by the terminal in the 5G network and that is sent by atleast one SMF+PGW-C, the HSS+UDM stores the session information of theestablished PDU session.

Optionally, if the switching indication information indicates whetherthe PDU session can be switched, and when the switching indicationinformation indicates that the PDU session can be switched to a 4Gnetwork, the HSS+UDM checks other PDU sessions with a same DNN as thePDU session. If the HSS+UDM stores other PDU sessions with a same DNN asthe PDU session, and one of these PDU sessions has been identified as“switchable” to the 4G network, the HSS+UDM determines which of the twoswitchable PDU sessions can be switched to the 4G network. The HSS+UDMmay determine, based on assistance information (referring to theforegoing assistance information), a PDU session that can be switched.If the HSS+UDM determines that a previously established PDU sessionindicated as “switchable” becomes non-switchable, the HSS+UDM notifiesan SMF+PGW-C corresponding to the PDU session of this change, and theSMF+PGW-C sets the PDU session to be non-switchable.

S607. The HSS+UDM may return response information to at least oneSMF+PGW-C, to indicate that the session information that is of the PDUsession and that is sent by the SMF+PGW-C is accepted.

S608. The SMF+PGW-C performs a PDU session establishment procedure, andthe SMF+PGW-C creates a context and sends the context to the AMF.

S609. The UE, an access network element, the AMF, the SMF+PGW-C, and thelike perform a subsequent PDU session establishment procedure. This stepbelongs to the prior art, and is not detailed herein.

S610. If the SMF+PGW-C modifies the switching indication information ofthe PDU session, the SMF+PGW-C sends modified switching indicationinformation to the terminal; or if the SMF+PGW-C does not modify theswitching indication information of the PDU session, the SMF+PGW-Creturns an acknowledgment message to the terminal, to indicate that theswitching indication information sent by the UE is accepted. Optionally,if the switching indication information is not modified by theSMF+PGW-C, the acknowledgment message may still carry the switchingindication information that is of the PDU session and that is sent bythe UE to the SMF+PGW-C.

S611. When the UE moves to a 4G network, if the UE establishes multiplePDU sessions with a same DNN, the UE determines a target PDU sessionbased on switching indication information of the multiple PDU sessionswith a same DNN, where the target PDU session is a PDU session that theUE expects to switch to 4G. When the switching indication informationindicates a switching priority, the UE determines a PDU session with ahighest priority in the multiple PDU sessions with a same DNN as thetarget PDU session; or when the switching indication informationindicates whether a PDU session can be switched, the UE determines, asthe target PDU session, a PDU session that “can be switched” to 4G andthat is indicated by the switching indication information.

S612. The UE sends a first request message to an MME, where the firstrequest message carries an ID of the target PDU session and a DNN of thetarget PDU session. The first request message may be an attach requestmessage, or may be a PDN connection establishment request message. TheID of the target PDU session is included in the PCO.

S613. If the first request message is the attach request message, afterreceiving the first request message, the MME sends a second requestmessage to the HSS+UDM, to request the session information from theHSS+UDM, where the session information may include a DNN and anSMF+PGW-C ID corresponding to the DNN.

S614. The HSS+UDM determines, from different PDU sessions with a sameDNN based on stored session information of the PDU sessions andswitching indication information of the PDU sessions with a same DNN, aPDU session with the DNN that can be switched, that is, a target PDUsession corresponding to the DNN, and determines an ID of an SMF+PGW-Ccorresponding to the target PDU session. When the switching indicationinformation indicates a switching priority, the HSS+UDM determines, asthe target PDU session, a PDU session with a highest priority in themultiple PDU sessions with a same DNN; or when the switching indicationinformation indicates whether a PDU session can be switched, the HSS+UDMdetermines, as the target PDU session, a PDU session that “can beswitched” to 4G and that is indicated by the switching indicationinformation.

S615. The HSS+UDM sends, to the MME, the DNN of the target PDU sessionand the SMF+PGW-C ID that are corresponding to the DNN. To be specific,the HSS+UDM stores session information of PDU sessions corresponding tomultiple DNNs, and the HSS+UDM may determine a target PDU sessioncorresponding to each DNN and an ID of an SMF+PGW-C corresponding to thetarget PDU session corresponding to the DNN. Then, the HSS+UDM sends, tothe MME, the DNN of the target PDU session corresponding to each DNN andthe ID of the SMF+PGW-C corresponding to the target PDU session. Forexample, the MME receives a DNN 1 and a corresponding SMF+PGW-C 1, and aDNN 2 and a corresponding SMF+PGW-C 2.

S616. After receiving the first request message sent by the UE, the MMEdetermines, based on the DNN that is of the target PDU session and thatis carried in the first request message, the DNN that is of the targetPDU session corresponding to each DNN and that is obtained in S615, andthe ID of the SMF+PGW-C corresponding to the target PDU session, theSMF+PGW-C ID corresponding to the DNN that is of the target PDU sessionand that is in the first request message, and determines an SMF+PGW-Cbased on the SMF+PGW-C ID.

S617. The MME sends a session establishment request message to theSMF+PGW-C, where the session establishment request message includes aPCO, and the PCO carries the ID of the target PDU session and the DNN ofthe target PDU session.

S618. The SMF+PGW-C determines, based on the ID and the DNN of thetarget PDU session that are sent by the MME, a PDU session that needs tobe switched. If the SMF+PGW-C stores the DNN and a session correspondingto the DNN, the SMF+PGW-C selects the PDU session for switching; or ifthe SMF+PGW-C finds that the target PDU session does not exist, theSMF+PGW-C rejects the PDU session.

FIG. 7A and FIG. 7B show a communication method 700 according to anembodiment of this application. The method 700 includes the followingsteps.

S701. UE sends a session establishment request message to an AMF.

S702. The AMF sends a session establishment request message to anSMF+PGW-C.

S703. The SMF+PGW-C determines switching indication information of a PDUsession. For example, the SMF+PGW-C may determine the switchingindication information of the PDU session based on the foregoingassistance information.

S704 is the same as S605. Optionally, the SMF+PGW-C may send theassistance information to an HSS+UDM, so that when finding thatswitching indication information from different SMF+PGW-Cs has aconflict, the HSS+UDM adjusts the conflict based on the assistanceinformation.

Optionally, S705, the HSS+UDM may adjust the switching indicationinformation of the PDU session. It is assumed that a priority of a PDUsession 1 that is received by the HSS UDM from the first SMF PGW-C is 2,and a priority of a PDU session 2 that is received by the HSS UDM fromthe second SMF PGW-C is also 2, and the PDU session 1 and the PDUsession 2 have a same DNN, then the HSS+UDM may adjust the priority ofthe PDU session 1 and/or the priority of the PDU session 2 based on theassistance information. For example, the HSS+UDM may adjust the priorityof the PDU session 2 to be higher or lower than the priority of the PDUsession 1.

S706. The HSS+UDM stores session information of the PDU session.

S707. If the HSS+UDM does not adjust the switching indicationinformation of the PDU session, the HSS+UDM sends response informationto the SMF+PGW-C, to indicate that the switching indication informationthat is of the PDU session and that is sent by the SMF+PGW-C isaccepted. Optionally, the response message may carry the acceptedswitching indication information of the PDU session. Alternatively, ifthe HSS+UDM adjusts the switching indication information of the PDUsession, the HSS+UDM adds adjusted switching indication information ofthe PDU session to a response message and sends the response message tothe SMF+PGW-C.

S708 to S718 are the same as S608 to S618.

FIG. 8A and FIG. 8B show a communication method 800 according to anembodiment of this application. The method 800 includes the followingsteps.

S801 is the same as S701.

S802 is the same as S702.

S803. The SMF+PGW-C sends assistance information, an SMF+PGW-C ID, and aDNN of a PDU session to an HSS+UDM, where the assistance information maybe the assistance information in the foregoing method.

S804. The HSS+UDM determines switching indication information of the PDUsession based on the received assistance information.

S805. The HSS+UDM stores the switching indication information of the PDUsession, the SMF+PGW-C ID, and the DNN of the PDU session.

S806. The HSS+UDM sends a response message to the SMF+PGW-C, where theresponse message carries the switching indication information of the PDUsession.

It should be understood that the HSS+UDM herein may receive assistanceinformation of PDU sessions, SMF+PGW-C IDs, DNNs of the PDU sessionsthat are sent by multiple SMF+PGW-Cs. The HSS+UDM sends, to eachSMF+PGW-C, determined switching indication information of a PDU sessioncorresponding to the SMF+PGW-C.

S807 to S817 are the same as S708 to S718.

FIG. 9 shows a communication method 900 according to an embodiment ofthis application. The method 900 includes the following steps.

Steps before S910 in the method 900 may be the same as S701 to S709 inthe method 700, or may be the same as S801 to S808 in the method 800.Herein, only steps after S910 in the method 900 are described.

S910. When the UE moves to a 4G network, the UE sends a first requestmessage to an MME, where the first request message carries a DNN of acurrent PDU session, and the first request message may be an attachrequest message or a session establishment request message.

S911 is the same as S812.

S912 is the same as S813.

S913 is the same as 814.

S914 is the same as S815.

S915. The MME sends a session establishment request message to theSMF+PGW-C, where the session establishment request message carries theDNN of the current PDU session.

S916. If there is only one PDU session corresponding to the DNN andbelonging to the SMF+PGW-C, the SMF+PGW-C determines the PDU session asa to-be-switched PDU session; or if there are multiple PDU sessionscorresponding to the DNN and belonging to the SMF+PGW-C, the SMF+PGW-Cmay determine one PDU session from the multiple PDU sessions as ato-be-switched PDU session.

S917. The SMF+PGW-C sends an identifier of the to-be-switched PDUsession to the UE, so that the UE associates the PDU session with a PDNconnection based on the identifier of the PDU session. Optionally, theidentifier of the PDU session is sent to the UE by using a PCO.

FIG. 6A to FIG. 9 show communication methods used when no N26 interfaceis deployed between the MME and the AMF. The following describes, withreference to FIG. 10A to FIG. 13, communication methods used when an N26interface is deployed between the MME and the AMF.

FIG. 10A and FIG. 10B show a communication method 1000 according to anembodiment of this application. The method 1000 includes the followingsteps.

S1001 is the same as S601.

S1002 is the same as S602.

S1003 is the same as S603.

S1004 is the same as S604.

S1005. The SMF+PGW-C stores the switching indication information of thePDU session.

S1006. The SMF+PGW-C sends a session establishment response message tothe AMF.

S1007 is the same as S609.

S1008. When the UE is in an idle state, and the UE moves to a 4Gnetwork, the UE may send a tracking area update (TAU) request message toan MME.

S1009. After receiving the TAU request message, the MME sends a firstcontext request message to the AMF, to request the AMF to send contextinformation of the UE to the MME, where the context information of theUE includes a session context.

S1010. After receiving the first context request message sent by theMME, the AMF sends a second context request message to the SMF+PGW-Cbased on the first context request message, to request a session contextfrom the SMF+PGW-C.

S1011. The SMF+PGW-C sends, to the AMF, session information of a PDUsession that can be switched to 4G. For example, the session informationincludes information such as switching indication information of the PDUsession, a default bearer identifier of a PDN connection correspondingto the PDU session, and a DNN and an SMF+PGW-C ID of the PDU session.

S1012. The AMF may receive session information that is of a PDU sessionand that is sent by each of multiple SMF+PGW-Cs, and the AMF maydetermine, from PDU sessions with a same DNN, a target PDU session as ato-be-switched PDU session based on the session information.

S1013. The AMF sends session information of the target PDU session tothe MME.

S1014. The MME, the AMF, the UE, and the like perform a subsequentswitching procedure. This step belongs to the prior art, and is notdetailed in this embodiment of this application.

FIG. 11A and FIG. 11B show a communication method 1100 according to anembodiment of this application. The method 1100 includes the followingsteps.

S1101 to S1107 are the same as S1001 to S1007.

S1108. When the UE is in a data connected state, and a gNB finds that alocation of the UE changes, the gNB sends a switching request to the AMFto request that a current PDU session needs to be switched.

S1109. The AMF sends a context request message to the SMF+PGW-C, toobtain a context of the UE.

S1110 is the same as S1011.

S1111 is the same as S1012.

S1112 is the same as S1013.

S1113 is the same as S1014.

FIG. 12 shows a communication method 1200 according to an embodiment ofthis application. The method 1200 includes the following steps.

Steps after S1204 in the method 1200 may be the same as S1008 to S1014in the method 1000, or may be the same as S1106 to S1113 in the method1100. Herein, only steps before S1204 in the method 1200 are described.

S1201 is the same as S801.

S1202 is the same as S802.

S1203. The SMF+PGW-C determines switching indication information of aPDU session based on assistance information of the PDU session. Forexample, the assistance information may be the foregoing assistanceinformation.

S1204 is the same as S1105.

FIG. 13 shows a communication method 1300 according to an embodiment ofthis application. The method 1300 includes the following steps.

Steps after S1305 in the method 1300 may be the same as S1006 to S1014in the method 1000, or may be the same as S1106 to S1113 in the method1100. Herein, only steps before S1305 in the method 1300 are described.

S1301 is the same as S801.

S1302 is the same as S802.

S1303. The SMF+PGW-C sends a session registration request message to anHSS+UDM, where the session registration request message includesassistance information, and the assistance information may be theforegoing assistance information.

S1304. The HSS+UDM receives the session registration request messagesent by the SMF+PGW-C, obtains the assistance information from thesession registration request message, and determines switchingindication information of a PDU session based on the assistanceinformation. In this way, the HSS+UDM can determine switching indicationinformation of PDU sessions corresponding to multiple SMF+PGW-Cs.

S1305. The HSS+UDM sends, to each SMF+PGW-C by using a response messageof the session registration request message, switching indicationinformation of a PDU session corresponding to the SMF+PGW-C.

It should be understood that sequences of steps in the method 200 to themethod 1300 are not limited in the embodiments of this application, andsequence numbers of steps in each method do not indicate a sequence. Inactual application, the sequence of the steps in each method can beadjusted. For example, the sequence of the steps in each method may bedetermined based on internal logic.

The foregoing details the communication methods in the embodiments ofthis application with reference to FIG. 1 to FIG. 13. The followingdetails communications apparatuses in the embodiments of thisapplication with reference to FIG. 14 to FIG. 19.

FIG. 14 shows a communications apparatus 1400 according to an embodimentof this application. The apparatus 1400 may be the foregoing networkdevice. The network device may be a user data management network elementor an access and mobility management function device. The apparatus 1400includes:

a processing unit 1410, configured to determine, based on switchingindication information of protocol data unit PDU sessions established bya terminal in a first network, a target PDU session from the establishedPDU sessions, where all the established PDU sessions have a same datanetwork name DNN; and

a transceiver unit 1420, configured to send session information of thetarget PDU session to a mobility management entity device in a secondnetwork.

In an optional embodiment, the switching indication information is usedto indicate a switching priority of each of the established PDUsessions. The processing unit 1410 is specifically configured todetermine, as the target PDU session, a PDU session with a highestswitching priority in the established PDU sessions.

In an optional embodiment, the switching indication information is usedto indicate whether each of the established PDU sessions can beswitched. The processing unit 1410 is specifically configured to: whenthe switching indication information indicates that there is only onePDU session that can be switched, determine the PDU session that can beswitched as the target PDU session; or when the switching indicationinformation indicates that there are at least two PDU sessions that canbe switched, determine the target PDU session from the at least two PDUsessions.

In an optional embodiment, the processing unit 1410 is specificallyconfigured to: if the at least two PDU sessions belong to a same controlplane function network element, determine each of the at least twosessions as the target PDU session; or if the at least two PDU sessionsbelong to different control plane function network elements, determinethe target PDU session from the at least two PDU sessions based onassistance information of each of the at least two PDU sessions.

In an optional embodiment, the apparatus 1400 is a user data managementnetwork element. The transceiver unit 1420 is further configured to:before the target PDU session is determined from the established PDUsessions based on the switching indication information of the protocoldata unit PDU sessions established by the terminal in the first network,receive assistance information that is of a first PDU session in theestablished PDU sessions and that is sent by a first control planefunction network element.

The processing unit 1410 is further configured to determine switchingindication information of the first PDU session based on the assistanceinformation.

In an optional embodiment, the assistance information includes at leastone of the following: an internet protocol IP address versioncorresponding to the PDU session, single network slice selectionassistance information corresponding to the PDU session, a session andservice continuity SSC mode corresponding to the PDU session, anallocation and retention priority ARP corresponding to the PDU session,a service type corresponding to the PDU session, and an establishmenttime corresponding to the PDU session.

In an optional embodiment, the transceiver unit 1420 is furtherconfigured to: before the target PDU session is determined from theestablished PDU sessions based on the switching indication informationof the protocol data unit PDU sessions established by the terminal inthe first network, receive the switching indication information that isof the PDU sessions established by the terminal in the first network andthat is sent by at least one control plane function network element.

In an optional embodiment, the apparatus 1400 is a user data managementnetwork element. The transceiver unit 1420 is further configured to:before the target PDU session is determined from the established PDUsessions based on the switching indication information of the protocoldata unit PDU sessions established by the terminal in the first network,receive initial switching indication information that is of a second PDUsession in the PDU sessions established by the terminal in the firstnetwork and that is sent by a second control plane function networkelement. The processing unit 1410 is further configured to adjust theinitial switching indication information to obtain switching indicationinformation of the second PDU session. The transceiver unit 1420 isfurther configured to send the switching indication information of thesecond PDU session to the second control plane function network element.

In an optional embodiment, the session information of the target PDUsession includes an identifier of a control plane function networkelement corresponding to the target PDU session and a DNN of the targetPDU session.

It should be understood that the apparatus 1400 herein is presented in aform of a function unit. The term “unit” herein may be an applicationspecific integrated circuit (ASIC), an electronic circuit, a processor(for example, a shared processor, a dedicated processor, or a groupprocessor) configured to execute one or more software or firmwareprograms, a memory, a combined logic circuit, and/or another appropriatecomponent that supports the described functions. In an optional example,a person skilled in the art may understand that the apparatus 1400 maybe specifically the network device in the foregoing method embodiment,and the apparatus 1400 may be configured to perform procedures and/orsteps corresponding to the network device in the foregoing methodembodiment. To avoid repetition, details are not described herein again.

FIG. 15 shows a communications apparatus 1500 according to an embodimentof this application. The apparatus 1500 may be the foregoing terminal.The apparatus 1500 includes: an obtaining unit 1510, configured toobtain switching indication information of protocol data unit PDUsessions established in a first network, where all the established PDUsessions have a same data network name DNN;

a processing unit 1520, configured to determine a target PDU sessionfrom the established PDU sessions based on the switching indicationinformation of the established PDU sessions; and

a transceiver unit 1530, configured to send an identifier of the targetPDU session to a first control plane function network element by using amobility management entity device in a second network.

In an optional embodiment, the switching indication information is usedto indicate a switching priority of each of the established PDUsessions. The processing unit 1520 is specifically configured todetermine, as the target PDU session, a PDU session with a highestswitching priority in the established PDU sessions.

In an optional embodiment, the switching indication information is usedto indicate whether each of the established PDU sessions can beswitched. The processing unit 1520 is specifically configured todetermine, as the target PDU session, a PDU session that can be switchedin the established PDU sessions.

In an optional embodiment, the transceiver unit 1530 is specificallyconfigured to send the identifier of the target PDU session and a DNN ofthe target PDU session to the mobility management entity device, wherethe DNN of the target PDU session is used by the mobility managemententity device to determine the first control plane function networkelement, so that the mobility management entity device sends theidentifier of the target PDU session to the first control plane functionnetwork element.

In an optional embodiment, the transceiver unit 1530 is specificallyconfigured to send a first request message to the mobility managemententity device, where the first request message carries the identifier ofthe target PDU session and the DNN of the target PDU session, and thefirst request message is an attach request message or a sessionestablishment request message.

In an optional embodiment, the obtaining unit 1510 is specificallyconfigured to receive the switching indication information of theestablished PDU sessions that is sent by at least one control planefunction network element.

In an optional embodiment, the transceiver unit 1530 is furtherconfigured to: send initial switching indication information of thefirst PDU session to a second control plane function network element,where the initial switching indication information is used to determineswitching indication information of the first PDU session; and receivethe switching indication information that is of the first PDU sessionand that is sent by the second control plane function network element.

It should be understood that the apparatus 1500 herein is presented in aform of a function unit. The term “unit” herein may be anapplication-specific integrated circuit (ASIC), an electronic circuit, aprocessor (for example, a shared processor, a dedicated processor, or agroup processor) configured to execute one or more software or firmwareprograms, a memory, a combined logic circuit, and/or another appropriatecomponent that supports the described functions. In an optional example,a person skilled in the art may understand that the apparatus 1500 maybe specifically the terminal in the foregoing method embodiment, and theapparatus 1500 may be configured to perform procedures and/or stepscorresponding to the terminal in the foregoing method embodiment. Toavoid repetition, details are not described herein again.

FIG. 16 shows a communications apparatus 1600 according to an embodimentof this application. The apparatus 1600 may be the foregoing firstcontrol plane function network element. The apparatus 1600 includes:

a transceiver unit 1610, configured to receive a session establishmentrequest message sent by a terminal, where the session establishmentrequest message is used to request to establish a first protocol dataunit PDU session; and

an obtaining unit 1620, configured to obtain switching indicationinformation of the first PDU session.

In an optional embodiment, the switching indication information is usedto indicate a priority of the first PDU session or used to indicatewhether the first PDU session can be switched.

In an optional embodiment, the session establishment request messageincludes the switching indication information of the first PDU session.The obtaining unit 1620 is specifically configured to obtain theswitching indication information of the first PDU session from thesession establishment request message. The transceiver unit 1610 isfurther configured to send the switching indication information of thefirst PDU session to a user data management network element or an accessand mobility management function device.

In an optional embodiment, the obtaining unit 1620 is specificallyconfigured to obtain initial switching indication information of thefirst PDU session. The apparatus 1600 further includes a processingunit, configured to obtain the switching indication information that isof the first PDU session and that is obtained through adjustment basedon the initial switching indication information. The transceiver unit1610 is further configured to send the switching indication informationof the first PDU session to the terminal, a user data management networkelement, or an access and mobility management function device.

In an optional embodiment, the transceiver unit 1610 is furtherconfigured to: send assistance information of the first PDU session to auser data management network element; receive the switching indicationinformation that is of the first PDU session and that is sent by theuser data management network element, where the switching indicationinformation of the first PDU session is determined based on theassistance information of the first PDU session, and the assistanceinformation of the first PDU session includes at least one of aninternet protocol IP address version corresponding to the first PDUsession, single network slice selection assistance informationcorresponding to the first PDU session, a session and service continuitySSC mode corresponding to the first PDU session, an allocation andretention priority ARP corresponding to the first PDU session, a servicetype corresponding to the first PDU session, and an establishment timecorresponding to the first PDU session; and send the switchingindication information of the first PDU session to the terminal or anaccess and mobility management function device.

In an optional embodiment, the transceiver unit 1610 is furtherconfigured to send a data network name DNN of the first PDU session andan identifier of the apparatus to the user data management networkelement.

It should be understood that the apparatus 1600 herein is presented in aform of a function unit. The term “unit” herein may be anapplication-specific integrated circuit (ASIC), an electronic circuit, aprocessor (for example, a shared processor, a dedicated processor, or agroup processor) configured to execute one or more software or firmwareprograms, a memory, a combined logic circuit, and/or another appropriatecomponent that supports the described functions. In an optional example,a person skilled in the art may understand that the apparatus 1600 maybe specifically the first control plane function network element or thesecond control plane function network element in the foregoing methodembodiment, and the apparatus 1600 may be configured to performprocedures and/or steps corresponding to the first control planefunction network element or the second control plane function networkelement in the foregoing method embodiment. To avoid repetition, detailsare not described herein again.

The apparatus 1400 is completely corresponding to the network device inthe method embodiments, the apparatus 1500 is completely correspondingto the terminal in the method embodiments, and the apparatus 1600 iscompletely corresponding to the first control plane function networkelement or the second control plane function network element in themethod embodiments. A corresponding unit performs a corresponding step.For example, the transceiver unit performs receiving and sending stepsin the method embodiments, and the processing unit may perform stepsother than the receiving and sending steps. For a function of a specificunit, refer to a corresponding method embodiment. Details are notdescribed again.

The apparatus 1400 to the apparatus 1600 in the foregoing solutions havefunctions of implementing corresponding steps performed by the networkdevice, the terminal, the first control plane function network element,or the second control plane function network element in the foregoingmethods, and the functions may be implemented by using hardware, or maybe implemented by hardware executing corresponding software. Thehardware or software includes one or more modules corresponding to theforegoing functions. For example, a sending unit may be replaced with atransmitter, a receiving unit may be replaced with a receiver, andanother unit such as a determining unit may be replaced with aprocessor, to separately perform a sending operation, a receivingoperation, and a related processing operation in the method embodiments.

In the embodiments of this application, the apparatuses in FIG. 14 toFIG. 16 each may be a chip or a chip system, for example, a system onchip (SoC). Correspondingly, the receiving unit and the sending unit maybe a transceiver circuit of the chip. This is not limited herein.

FIG. 17 shows still another communications apparatus 1700 according toan embodiment of this application. The apparatus 1700 includes aprocessor 1710, a transceiver 1720, and a memory 1730. The processor1710, the transceiver 1720, and the memory 1730 communicate with eachother through an internal connection path. The memory 1730 is configuredto store an instruction. The processor 1710 is configured to execute theinstruction stored in the memory 1730, to control the transceiver 1720to send a signal and/or receive a signal.

The processor 1710 is configured to determine, based on switchingindication information of protocol data unit PDU sessions established bya terminal in a first network, a target PDU session from the establishedPDU sessions, where all the established PDU sessions have a same datanetwork name DNN. The transceiver 1720 is configured to send sessioninformation of the target PDU session to a mobility management entitydevice in a second network.

It should be understood that the apparatus 1700 may be specifically thenetwork device in the foregoing method embodiment, and may be configuredto perform steps and/or procedures corresponding to the network devicein the foregoing method embodiment. Optionally, the memory 1730 mayinclude a read-only memory and a random access memory, and provide aninstruction and data for the processor. A part of the memory may furtherinclude a nonvolatile random access memory. For example, the memory mayfurther store device type information. The processor 1710 may beconfigured to execute the instruction stored in the memory. In addition,when the processor 1710 executes the instruction stored in the memory,the processor 1710 is configured to perform the steps and/or procedurescorresponding to the network device in the foregoing method embodiment.

FIG. 18 shows still another communications apparatus 1800 according toan embodiment of this application. The apparatus 1800 includes aprocessor 1810, a transceiver 1820, and a memory 1830. The processor1810, the transceiver 1820, and the memory 1830 communicate with eachother through an internal connection path. The memory 1830 is configuredto store an instruction. The processor 1810 is configured to execute theinstruction stored in the memory 1830, to control the transceiver 1820to send a signal and/or receive a signal.

The transceiver 1820 is configured to obtain switching indicationinformation of protocol data unit PDU sessions established in a firstnetwork, where all the established PDU sessions have a same data networkname DNN. The processor 1810 is configured to determine a target PDUsession from the established PDU sessions based on the switchingindication information of the established PDU sessions. The transceiver1820 is configured to send an identifier of the target PDU session to afirst control plane function network element by using a mobilitymanagement entity device in a second network.

It should be understood that the apparatus 1800 may be specifically theterminal in the foregoing method embodiment, and may be configured toperform steps and/or procedures corresponding to the terminal in theforegoing method embodiment. Optionally, the memory 1830 may include aread-only memory and a random access memory, and provide an instructionand data for the processor. A part of the memory may further include anonvolatile random access memory. For example, the memory may furtherstore device type information. The processor 1810 may be configured toexecute the instruction stored in the memory. In addition, when theprocessor 1810 executes the instruction stored in the memory, theprocessor 1810 is configured to perform the steps and/or procedurescorresponding to the terminal in the foregoing method embodiment.

FIG. 19 shows still another communications apparatus 1900 according toan embodiment of this application. The apparatus 1900 includes aprocessor 1910, a transceiver 1920, and a memory 1930. The processor1910, the transceiver 1920, and the memory 1930 communicate with eachother through an internal connection path. The memory 1930 is configuredto store an instruction. The processor 1910 is configured to execute theinstruction stored in the memory 1930, to control the transceiver 1920to send a signal and/or receive a signal.

The transceiver 1920 is configured to receive a session establishmentrequest message sent by a terminal, where the session establishmentrequest message is used to request to establish a first protocol dataunit PDU session. The transceiver 1920 is further configured to obtainswitching indication information of the first PDU session.

It should be understood that the apparatus 1900 may be specifically thefirst control plane function network element or the second control planefunction network element in the foregoing method embodiment, and may beconfigured to perform steps and/or procedures corresponding to the firstcontrol plane function network element or the second control planefunction network element in the foregoing method embodiment. Optionally,the memory 1930 may include a read-only memory and a random accessmemory, and provide an instruction and data for the processor. A part ofthe memory may further include a nonvolatile random access memory. Forexample, the memory may further store device type information. Theprocessor 1910 may be configured to execute the instruction stored inthe memory. In addition, when the processor 1910 executes theinstruction stored in the memory, the processor 1910 is configured toperform the steps and/or procedures corresponding to the core networkelement in the first network in the foregoing method embodiment.

It should be understood that the transceiver may include a transmitterand a receiver. The transceiver may further include an antenna, wherethere may be one or more antennas. The memory may be an independentdevice, or may be integrated into the processor. All or some of theforegoing components may be integrated into a chip for implementation,for example, integrated into a baseband chip for implementation.

In the embodiments of this application, alternatively, the transceiversin FIG. 17 to FIG. 19 each may be a communications interface. This isnot limited herein.

In the embodiments of this application, the first control plane functionnetwork element or the second control plane function network element maybe a physical entity device, or may be a virtual function networkelement. This is not limited herein.

In the embodiments of this application, for ease of understanding,multiple examples are used for description. However, these examples aremerely examples, and this does not mean that the examples are bestimplementations for implementing this application.

In the embodiments of this application, for ease of description, therequest message, the response message, and various other message namesare used. However, these messages are merely used as examples todescribe content that needs to be carried or a function that needs to beimplemented. A specific name of the message is not limited in thisapplication. For example, the message may be a first message, a secondmessage, or a third message. These messages may be some specificmessages, or may be some fields in a message. These messages may alsorepresent various service operations.

It should also be understood that, the processor in the foregoingapparatus in the embodiments of this application may be a centralprocessing unit (CPU), or the processor may be another general purposeprocessor, a digital signal processor (DSP), an application-specificintegrated circuit (ASIC), a field-programmable gate array (FPGA) oranother programmable logic device, a discrete gate or a transistor logicdevice, a discrete hardware component, or the like. The general purposeprocessor may be a microprocessor, or the processor may be anyconventional processor or the like.

In an implementation process, steps in the foregoing methods can becompleted by using a hardware integrated logical circuit in theprocessor, or by using instructions in a form of software. The steps inthe method disclosed with reference to the embodiments of thisapplication may be directly performed by a hardware processor, or may beperformed by using a combination of hardware in the processor and asoftware unit. A software unit may be located in a mature storage mediumin the art, such as a random access memory, a flash memory, a read-onlymemory, a programmable read-only memory, an electrically erasableprogrammable memory, a register, or the like. The storage medium islocated in the memory, and the processor executes instructions in thememory and completes the steps in the foregoing methods in combinationwith the hardware in the processor. To avoid repetition, details are notdescribed herein again.

All or some of the foregoing embodiments may be implemented by usingsoftware, hardware, firmware, or any combination thereof. When softwareis used to implement the embodiments, the embodiments may be implementedcompletely or partially in a form of a computer program product. Thecomputer program product includes one or more computer instructions.When the computer program instruction is loaded and executed on acomputer, the procedure or functions according to the embodiments ofthis application are all or partially generated. The computer may be ageneral purpose computer, a dedicated computer, a computer network, oranother programmable apparatus. The computer instruction may be storedin a computer readable storage medium or may be transmitted from acomputer readable storage medium to another computer readable storagemedium. For example, the computer instruction may be transmitted from awebsite, computer, server, or data center to another website, computer,server, or data center in a wired (for example, a coaxial cable, anoptical fiber, or a digital subscriber line (DSL)) or wireless (forexample, infrared, radio, or microwave) manner. The computer readablestorage medium may be any usable medium accessible by a computer, or adata storage device, such as a server or a data center, integrating oneor more usable media. The usable medium may be a magnetic medium (forexample, a floppy disk, a hard disk, or a magnetic tape), an opticalmedium (for example, a DVD), a semiconductor medium (for example, asolid state disk (SSD)), or the like.

A person of ordinary skill in the art may be aware that, in combinationwith the examples described in the embodiments disclosed in thisspecification, units and algorithm steps may be implemented by usingelectronic hardware or a combination of computer software and electronichardware. Whether the functions are performed by hardware or softwaredepends on particular applications and design constraints of thetechnical solutions. A person skilled in the art may use a differentmethod to implement the described functions for each particularapplication, but it should not be considered that the implementationgoes beyond the scope of this application.

It may be clearly understood by a person skilled in the art that for thepurpose of convenient and brief description, for a detailed workingprocess of the foregoing system, apparatus, and unit, refer to acorresponding process in the foregoing method embodiments. Details arenot described herein again.

In the several embodiments provided in this application, it should beunderstood that the disclosed system, apparatus, and method may beimplemented in other manners. For example, the described apparatusembodiments are merely examples. For example, the unit division ismerely logical function division and may be other division in actualimplementation. For example, multiple units or components may becombined or integrated into another system, or some features may beignored or not be performed. In addition, the displayed or discussedmutual couplings or direct couplings or communication connections may beimplemented through some interfaces. The indirect couplings orcommunication connections between the apparatuses or units may beimplemented in electrical, mechanical, or other forms.

The units described as separate parts may or may not be physicallyseparate, and parts displayed as units may or may not be physical units,may be located in one position, or may be distributed on multiplenetwork units. Some or all of the units may be selected depending onactual requirements to achieve the objectives of the solutions of theembodiments.

In addition, function units in the embodiments of this application maybe integrated into one processing unit, each of the units may existalone physically, or at least two units are integrated into one unit.

When the functions are implemented in a form of a software function unitand sold or used as an independent product, the functions may be storedin a computer readable storage medium. Based on such an understanding,the technical solutions of this application essentially, or the partcontributing to the prior art, or some of the technical solutions may beimplemented in a form of a software product. The computer softwareproduct is stored in a storage medium, and includes several instructionsfor instructing a computer device (which may be a personal computer, aserver, a network device, or the like) to perform all or some of thesteps in the methods described in the embodiments of this application.The foregoing storage medium includes: any medium that can store programcode, such as a USB flash drive, a removable hard disk, a read-onlymemory (ROM), a random access memory (RAM), a magnetic disk, or anoptical disc.

The foregoing descriptions are merely specific implementations of thisapplication, but are not intended to limit the protection scope of thisapplication. Any variation or replacement readily figured out by aperson skilled in the art within the technical scope disclosed in thisapplication shall fall within the protection scope of this application.Therefore, the protection scope of this application shall be subject tothe protection scope of the claims.

What is claimed is:
 1. A communication method, comprising: determining,by a network device based on switching indication information ofestablished protocol data unit (PDU) sessions of a terminal in a firstnetwork, a target PDU session from the established PDU sessions, whereinthe established PDU sessions have a same data network name (DNN); andsending, by the network device, session information of the target PDUsession to a mobility management entity device in a second network;receiving, by the mobility management entity device from the networkdevice, the session information of the target PDU session.
 2. The methodaccording to claim 1, wherein the switching indication information ofthe established PDU sessions indicates at least one PDU session which isswitchable in the established PDU sessions.
 3. The method according toclaim 1, wherein the determining the target PDU session from theestablished PDU sessions comprises: determining, by the network devicewhen the switching indication information indicates of the establishedPDU sessions that there is only one PDU session that is switchable, theonly one PDU session as the target PDU session.
 4. The method accordingto claim 1, wherein the determining the target PDU session from theestablished PDU sessions comprises: determining, by the network devicewhen the switching indication information of the established PDUsessions indicates that there are at least two PDU sessions that areswitchable, the target PDU session from the at least two PDU sessions.5. The method according to claim 4, wherein the determining the targetPDU session from the at least two PDU sessions comprises: determining,by the network device, whether the at least two PDU sessions belong to asame control plane function network element; in response to determiningthat the at least two PDU sessions belong to a same control planefunction network element, determining, by the network device, each ofthe at least two sessions as the target PDU session; or in response todetermining that the at least two PDU sessions belong to differentcontrol plane function network elements, determining, by the networkdevice, the target PDU session from the at least two PDU sessions basedon assistance information of each of the at least two PDU sessions. 6.The method according to claim 1, wherein the method comprises:receiving, by a first control plane function network element, a sessionestablishment request message from a terminal, wherein the sessionestablishment request message is used to request to establish a firstPDU session; determining, by the first control plane function networkelement, switching indication information of the first PDU session;sending, by the first control plane function network element, theswitching indication information of the first PDU session to the networkdevice; receiving, by the network device, the switching indicationinformation of the first PDU session.
 7. The method according to claim6, wherein the determining, by the first control plane function networkelement, switching indication information of the first PDU sessioncomprises: obtaining, by the first control plane function networkelement, initial switching indication information of the first PDUsession; and determining, by the first control plane function networkelement, the switching indication information of the first PDU sessionbased on the initial switching indication information.
 8. The methodaccording to claim 1, wherein the session information of the target PDUsession comprises an identifier of a control plane function networkelement corresponding to the target PDU session and a DNN of the targetPDU session.
 9. The method according to claim 1, the method furthercomprising: receiving, by the mobility management entity device, anattach request from the terminal; sending, by the mobility managemententity device, a request message to the network device to get sessioninformation of the terminal.
 10. The method according to claim 1,wherein the network device is a user data management network element.11. A communication system, comprising: a network device; and a mobilitymanagement entity device in a second network, wherein the network deviceis configured to: determine, based on switching indication informationof established protocol data unit (PDU) sessions of a terminal in afirst network, a target PDU session from the established PDU sessions,wherein the established PDU sessions have a same data network name(DNN); and send session information of the target PDU session to themobility management entity device; the mobility management entity deviceis configured to: receive the session information of the target PDUsession from the network device.
 12. The system according to claim 11,wherein the switching indication information of the established PDUsessions indicates at least one PDU session which is switchable in theestablished PDU sessions.
 13. The system according to claim 11, whereinthe network device is configured to: determine, when the switchingindication information of the established PDU sessions indicates thatthere is only one PDU session that is switchable, the only one PDUsession as the target PDU session.
 14. The system according to claim 11,wherein the network device is configured to: determining, when theswitching indication information of the established PDU sessionsindicates that there are at least two PDU sessions that are switchable,the target PDU session from the at least two PDU sessions.
 15. Thesystem according to claim 14, wherein the network device is configuredto: determine whether the at least two PDU sessions belong to a samecontrol plane function network element; in response to determining thatthe at least two PDU sessions belong to a same control plane functionnetwork element, determine each of the at least two sessions as thetarget PDU session; or in response to determining that the at least twoPDU sessions belong to different control plane function networkelements, determine the target PDU session from the at least two PDUsessions based on assistance information of each of the at least two PDUsessions.
 16. The system according to claim 11, wherein the systemfurther comprising a first control plane function network element;wherein first control plane function network element is configured to:receive a session establishment request message from a terminal, whereinthe session establishment request message is used to request toestablish a first PDU session; determine switching indicationinformation of the first PDU session; send the switching indicationinformation of the first PDU session to the network device; the networkdevice is configured to: receive the switching indication information ofthe first PDU session.
 17. The system according to claim 11, whereinfirst control plane function network element is further configured to:obtain initial switching indication information of the first PDUsession; and determine the switching indication information of the firstPDU session based on the initial switching indication information. 18.The system according to claim 11, wherein the session information of thetarget PDU session comprises an identifier of a control plane functionnetwork element corresponding to the target PDU session and a DNN of thetarget PDU session.
 19. The system according to claim 11, wherein themobility management entity device is further configured to: receive anattach request from the terminal; send a request message to the networkdevice to get session information of the terminal.
 20. The systemaccording to claim 11, wherein the network device is a user datamanagement network element.